Hindawi Publishing Corporation Abstract and Applied Analysis Volume 2008, Article ID 581582, 11 pages doi:10.1155/2008/581582 Research Article Euler Numbers and Polynomials Associated with Zeta Functions Taekyun Kim Division of General Education-Mathematics, Kwangwoon University, Seoul 139-701, South Korea Correspondence should be addressed to Taekyun Kim, tkim@knu.ac.kr Received 16 January 2008; Accepted 19 April 2008 Recommended by Lance Littlejohn zeta function and the Euler zeta function are defined by For s ∈ C , the Euler Hurwitz-type n n s ∞ s ζE s 2 ∞ n1 −1 /n , and ζE s, x 2 n0 −1 /n x . Thus, we note that the Euler zeta functions are entire functions in whole complex s-plane, and these zeta functions have the values of the Euler numbers or the Euler polynomials at negative integers. That is, ζE −k Ek∗ , and ζE −k, x Ek∗ x. We give some interesting identities between the Euler numbers and the zeta functions. Finally, we will give the new values of the Euler zeta function at positive even integers. Copyright q 2008 Taekyun Kim. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction Throughout this paper, Z, Q, C, Zp , Qp , and Cp will, respectively, denote the ring of rational integers, the field of rational numbers, the field of complex numbers, the ring p-adic rational integers, the field of p-adic rational numbers, and the completion of the algebraic closure of Qp . Let vp be the normalized exponential valuation of Cp such that |p|p p−vp p p−1 . If q ∈ Cp , we normally assume that |q − 1|p < 1. We use the notation 1 − qx 1 − −qx , x−q . 1.1 1−q 1q Hence, limq→1 xq 1, for any x with |x|p ≤ 1 in the present p-adic case. Let p be a fixed odd prime. For d odd, a fixed positive integer with p, d 1, let Z X Xd lim , X1 Zp , X∗ a dpZp ← N 0<a<dp N dp Z 1.2 a,p1 N n a dp Zp x ∈ X | x ≡ a mod dp , xq where a ∈ Z lies in 0 ≤ a < dpN . 2 Abstract and Applied Analysis In 1, we note that −qa −1a qa μ−q a dpN Zp 1 q N dpN −q 1 qdp 1.3 is distribution on X for q ∈ Cp with |1 − q|p < 1. This distribution yields an integral as follows: −1 p 1 I−q f fxdμ−q x lim N fx−qx , N→∞ p Zp −q x0 N for f ∈ UD Zp , 1.4 which has a sense as we see readily that the limit is convergent see 1. Let q 1. Then, we have the fermionic p-adic integral on Zp as follows: I−1 f Zp fxdμ−1 x lim N −1 p N→∞ fx−1x , 1.5 x0 cf. 1–5. For any positive integer N, we set qa μq a lpN Zp N lp q 1.6 cf. 1–3, 6–20 and this can be extended to a distribution on X. This distribution yields p-adic bosonic q-integral as follows see 11, 20: Iq f fxdμq x fxdμq x, 1.7 Zp X where f ∈ UDZp the space of uniformly differentiable function on Zp with values in Cp , cf. 2, 11, 16–20. In view of notation, I−1 can be written symbolically as I−1 f limq→−1 Iq f. If we take fx q−x xnq , then we can derive the q-extension of Bernoulli numbers and polynomials from p-adic q-integrals on Zp as follows: βn,q Zp q−x xnq dμq x, βn,q x Zp q−y y xq dμq y 1.8 i m , i iq 1.9 cf. 11, 20. Thus, we note that β0,q q−1 , log q βm,q m 1 m q − 1 i0 cf. 11, 14, 20. In the complex plane, the ordinary Bernoulli numbers are a sequence of signed rational numbers that can be defined by the identity ∞ t tn B , n et − 1 n0 n! cf. 1–33. |t| < 2π 1.10 Taekyun Kim 3 These numbers arise in the series expansions of trigonometric functions, and are extremely important in number theory and analysis. From the generating function of Bernoulli numbers, we note that B0 1, B1 −1/2, B2 1/6, B4 −1/30, B6 1/42, B8 −1/30, B10 5/66, B12 −691/2730, B14 7/6, B16 −3617/510, B18 43867/798, B20 −174611/330, . . . , and B2k1 0 for k ∈ N. It is well known that Riemann zeta function is defined by ζs ∞ 1 , s n n1 for s ∈ C. 1.11 We also note that the Riemann zeta function is closely related to Bernoulli numbers at positive integer or negative integer in the complex plane. Riemann did develop the theory of analytic continuation needed to rigorously define ζs for all s ∈ C − {0}. From this zeta function, he derived the following formula cf. 1–33: ζ−n − Bn1 , n1 n ∈ N {1, 2, 3, . . .}. 1.12 Thus, we note that ζ−n 0 if n is an even integer and greater than 0. These are called the trivial zeros of the zeta function. In 1859, starting with Euler’s factorization of the zeta function ζs 1 , 1 − p −s p:prime 1.13 he derived an explicit formula for the prime numbers in terms of zeros of the zeta function. He also posed the Riemann hypothesis: if ζz 0, then either z is a trivial zero or z lies on the critical line Rez 1/2 cf. 4, 5, 16–20, 27–33. It is well known that sin z z z2 z3 z2 1− 1 − .... 1− 2 π 2π2 3π2 1.14 Thus, 1 − z cot z 2 ∞ ζ2m m1 π 2m 1.15 z2m cf. 4, 5, 10, 16–20, 27–33. From this, we can derive the following famous formula. Lemma 1.1. For n ∈ N, ζ2n ∞ 1 −1n−1 2π2n B2n , 22n! k 2n k1 for n ∈ N. 1.16 It is easy to see that z cot z ∞ 2iz −1k 22k B2k 2k iz 1 z . 2k! e2iz − 1 k1 1.17 4 Abstract and Applied Analysis However, it is not known the values of ζ2k 1 for k ∈ N. In the case of k 1, Apery proved that ζ3 is irrational number see 34. The constants Ek∗ in the Taylor series expansion et ∞ tn 2 En∗ , 1 n0 n! where |t| < π 1.18 cf. 3–5, 10, 27 are known as the first-kind Euler numbers. From the generating function of the first-kind Euler numbers, we note that n n ∗ ∗ E0 1, En − 1.19 El∗ , for n ∈ N. l l0 ∗ The first few are 1, − 1/2, 0, 1/4, . . . , and E2k 0 for k 1, 2, . . . . The Euler polynomials are also defined by ∞ ∞ n 2 tn tn n xt ∗ ∗ n−k . 1.20 e En x Ek x t n! n0 k0 k n! e 1 n0 For s ∈ C, the Euler zeta function and Hurwitz’s type Euler zeta function are defined by ζE s 2 ∞ −1n n1 ns ζE s, x 2 , ∞ −1n s n0 n x 1.21 cf. 2, 4, 5, 9, 10, 27. Thus, we note that Euler zeta functions are entire functions in the whole complex s-plane and these zeta functions have the values of the Euler numbers or Euler polynomials at negative integers. That is, ζE −k Ek∗ , ζE −k, x Ek∗ x 1.22 cf. 2, 4, 5, 9, 10, 27. In this paper, we give some interesting identities between Euler numbers and zeta functions. Finally, we will give the values of the Euler zeta function at positive even integers. 2. Preliminaries/Euler numbers associated with p-adic fermionic integrals Let f1 x be the translation defined by f1 x fx 1. Then we have I−1 f1 −I−1 f 2f0. 2.1 If we take fx exyt , then we can derive the first-kind Euler polynomials from the integral equation of I−1 f as follows: Zp exyt dμ−1 y ext et ∞ En∗ xtn 2 . 1 n0 n! 2.2 That is, Zp y n dμ−1 y En∗ , Zp x yn dμ−1 y En∗ x. 2.3 Taekyun Kim 5 For n ∈ N, we have the following integral equation: Zp fx ndμ−1 x −1n−1 Zp fxdμ−1 x 2 n−1 −1n−1l fl. 2.4 l0 From this we note that Ek∗ n − Ek∗ 2 n−1 −1l−1 lk , if n ≡ 0 mod 2, l0 Ek∗ n Ek∗ 2 n−1 2.5 l k −1 l , if n ≡ 1 mod 2. l0 Let fx sin ax or fx cos ax. By using the fermionic p-adic q-integral on Zp , we see that 0 sin ax dμ−1 x sin ax dμ−1 x Zp Zp cos a 1 sin ax dμ−1 x sin a cos ax dμ−1 x, Zp 2.6 Zp see 12, 2 cos a 1 cos ax dμ−1 x − sin a sin ax dμ−1 x. Zp Zp 2.7 Thus, we obtain Zp cos ax dμ−1 x 1, Zp sin ax dμ−1 x − sin a , cos a 1 2.8 ∗ . E2n1 2.9 see 12. From this we note that tan a − 2 Zp sin ax dμ−1 x ∞ −1n1 a2n1 n0 2n 1! By the same motivation, we can also observe that a a cot 2 2 Zp cos ax dμ1 x ∞ −1n B2n n0 2n! a2n , 2.10 see 12. These formulae are also treated in Section 3. Let fx et2x1 . Then we can derive the generating function of the second-kind Euler numbers from fermionic p-adic integral equation as follows: Zp et2x1 dμ−1 x et ∞ tn 2 1 En . −t cosh t n0 n! e 2.11 6 Abstract and Applied Analysis Thus, we have E 1n E − 1n 2δ0,n , 2.12 where we have used the symbolic notation En for En . The first few are E0 1, E1 0, E2 −1, E3 0, E4 5, . . ., E2k1 0 for k ∈ N. In particular, E2n − n−1 k0 2n E2k . 2k 2.13 Recently, Simsek, Ozden, Cangül, Cenkci, Kurt, and others have studied the various extensions of the first kind Euler numbers by using fernionic p-adic invariant q-integral on Zp , see 2– 5, 16, 20, 27. It seems to be also interesting to study the q-extensions of the second-kind Euler numbers due to Simsek et al. see 4, 5, 16. 3. Some relationships between Euler numbers and zeta functions In this section, we also consider Bernoulli and the second Euler numbers in the complex plane. The second-kind Euler numbers Ek are defined by the following expansion: sech x ∞ xk 1 2ex Ek , 2x cosh x e 1 k0 k! for |x| < π 2 3.1 cf. 10. From 1.18 and 3.1, we can derive the following equation: k Ek 2l El∗ , l l0 k k where is binomial coefficient. l 3.2 By 3.2 and 1.18, we easily see that E0 1, E1 0, E2 −1, E3 0, E4 5, E6 61, . . . , and E2k1 0 for k 1, 2, 3, . . . . As Euler formula, it is well known that eix cos x i sin x, where i −11/2 . 3.3 From 3.3, we note that cos x eix e−ix /2. Thus, we have sec x ∞ n i En n 2 sechix x ix −ix n! e e n0 ∞ −1n E2n n0 2n! x 2n ∞ ∞ −1n E2n1 2n1 −1n E2n 2n i x x . 2n 1! 2n! n0 n0 3.4 From 3.4, we derive x sec x ∞ −1n E2n n0 2n! x2n1 , for |x| < π . 2 3.5 Taekyun Kim 7 The Fourier series of an odd function on the interval −p, p is the sine series: ∞ fx nπx , p 3.6 nπx dx. p 3.7 bn sin n1 where 2 bn p p fx sin 0 Let us consider fx sin ax on −π, π. From 3.6 and 3.7, we note that sin ax ∞ 3.8 bn sin nx, n1 where π π cosn − ax − cosn ax dx 2 0 0 1 sinn − ax sinn ax π n n−1 2 . −1 − sin aπ π n−a na π n2 − a2 0 bn 2 π 2 π sin ax sin nx dx 3.9 In 3.8, if we take x π/2, then we have sin ∞ ∞ πa 2n − 1 2 b2n−1 −1n−1 sin aπ −1n−1 2 π 2n − 12 − a2 n1 n1 ∞ ∞ ∞ 2 2n − 1−1n−1 −1n−1 a2k 2 sin aπ sin aπ 2 2 π π 2n − 1 k0 2n − 12k n1 2n − 1 1 − a/2n − 1 n1 ∞ ∞ −1n−1 2 sin aπ a2k 2k1 π 2n − 1 k0 n1 3.10 From 3.10, we note that πa sec 2 πa 2 ∞ ∞ 2 k0 −1n−1 2k1 n1 2n − 1 a2k1 . 3.11 In 3.5, it is easy to see that πa sec 2 πa 2 ∞ −1n E2n π 2n1 n0 2n! 2 a2n1 . 3.12 By 3.11 and 3.12, we obtain the following. Theorem 3.1. For n ∈ N, ∞ −1k−1 k1 2k − 12n1 ∞ −1k k0 2k 12n1 −1n 2n1 π E2n . 22n! 2 3.13 8 Abstract and Applied Analysis It is easy to see that ∞ −1n n1 2n 12k1 2 ∞ 1 ∞ 1 − ∞ 1 −1 2k1 n1 n − 32k1 n1 2n2k1 22k1 − 1 1 1 − 4k1 ζ 2k 1, ζ2k 1 − 1. 4 2 22k1 n1 4n 3.14 By 3.13 and 3.14, we obtain the following. Corollary 3.2. For n ∈ N, E2n 1 22n 1 − 22n1 ζ2n 1 −1n π 2n1 22n . ζ 2n 1, 4 22n! 3.15 By simple calculation, we easily see that i tan x eix − e−ix 2 4 1 − 2ix . eix e−ix e − 1 e4ix − 1 3.16 Thus, we have ∞ −1n B 4n 1 − 4n 2xi 4xi 2n x2n . x tan x −xi 2xi − 2n! e − 1 e4xi − 1 n1 3.17 From 3.17, we can easily derive ∞ −1n1 4n1 1 − 4n1 B 2n2 2n1 x tan x . 2n 2! n0 3.18 By 3.3, we also see that i tan x 1 − ∗ ∞ E2n1 2 i 22n1 −1n1 x2n1 . 2n 1! e2ix 1 n0 3.19 Thus, we have tan x ∗ ∞ E2n1 22n1 −1n1 x2n1 . 2n 1! n0 3.20 By 3.18 and 3.20, we obtain the following. Theorem 3.3. For n ∈ N, ∗ −1n−1 2π2n E2n−1 ζ2n , 42n − 1! 1 − 4n where En∗ are the first-kind Euler numbers. 3.21 Taekyun Kim 9 It is easy to see that ∞ 1 k1 2k 12n −1n 2π2n ∗ 1 1 − n ζ2n n1 . E 4 4 2n − 1! 2n−1 3.22 Therefore, we obtain the following corollary. Corollary 3.4. For n ∈ N, ∞ 1 k1 2k 12n −1n 2π2n ∗ . E 4n1 2n − 1! 2n−1 3.23 Now we try to give the new value of the Euler zeta function at positive integers. From the definition of the Euler zeta function, we note that ζE s 2 ∞ −1n n1 ns −2 ∞ 1 1 s s−1 ζs, 2 2n 1 n0 s ∈ C. 3.24 By 3.24, Theorem 3.3, and Corollary 3.4, we obtain the following theorem. Theorem 3.5. For n ∈ N, −1n−1 π 2n 2 − 4n ∗ ζE 2n E2n−1 . 22n − 1! 1 − 4n 3.25 Remark 3.6. We note that ζ2 π 2 /6, ζE 2 −π 2 /6, ζ4 π 4 /90 and ζE 4 −7π 4 /360 . . .. For q ∈ C with |q| < 1, s ∈ C, q-ζ-function is defined by ζq s s ∞ qn 1 1 − q s − s − 1 log q n1 nq 3.26 cf. 10, 14. Note that ζq s is analytic continuation in C with only one simple pole at s 1, and ζq 1 − k − βk,q , k where k is a positive integer 3.27 cf. 14. By simple calculation, we easily see that ∞ θ 2j1 n2j1 ∞ −1n qn q n1 n2k1 q j0 2j 1! k−1 k−1 1 − q2k−2j 1 − q2k−2j 1 1 − log q j0 2k − 2j − 12j 1! log q j0 2k − 2j − 12j 1! k−1 ∞ q θ 2k1 −1j θ 2j1 θ 2j1 −1j H2j−2k,q −q−1 2 −ζq 2k−2jζq2 2k−2j 2k−2j − −1k , 2j 1! 1q 2k1! 2j 1! 1q 2 j0 jk1 q 3.28 10 Abstract and Applied Analysis where Hn,q −q are Carlitz’s q-Euler numbers with limq→1 Hn,q −q En∗ cf. 6, 21, 22. If q→1, then we have ∞ −1n n1 n2k1 sinnθ 2k−2j k−1 2 −1j 2j1 1 θ 2k1 k−j1 2π θ B −1k . − 1 × −1 − 2k−2j 2k−2j 2j 1! 2 · 2k − 2j! 2 2k 1! 2 j0 3.29 For k ∈ N, and θ π/2, it is easy to see that ∞ −1n n1 2n − 12k1 k−1 −1k π 2k1 22k−2j − 2 B 2k−2j j0 2j 1!2k − 2j!22j2 − π 2k1 −1k . 2k 1!22k2 3.30 From 3.30 and Theorem 3.1, we can also derive the following equation: k−1 −1k−1 π 2k1 22k−2j − 2 B 2k−2j j0 2j 1!2k − 2j!22j2 2k1 π π 2k1 −1k k E2k −1 . 22k! 2 2k 1!22k2 3.31 1 E2k − 2k2 . 2k2 2k 1!2 2 2k! 3.32 Thus, we have k−1 j0 2j 22k−2j − 2 B2k−2j 1!2k − 2j!22j2 Acknowledgments The present research has been conducted by the research grant of Kwangwoon University in 2008. The author wishes to express his sincere gratitude to the referees and Professor Lance L. Littlejohn for their valuable suggestions and comments. References 1 T. Kim, “A note on p-adic q-integral on Zp associated with q-Euler numbers,” Advanced Studies in Contemporary Mathematics, vol. 15, no. 2, pp. 133–137, 2007. 2 I. N. 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