

A000061


Generalized tangent numbers d(n,1).
(Formerly M0938 N0352)


5



1, 1, 2, 4, 4, 6, 8, 8, 12, 14, 14, 16, 20, 20, 24, 32, 24, 30, 38, 32, 40, 46, 40, 48, 60, 50, 54, 64, 60, 68, 80, 64, 72, 92, 76, 96, 100, 82, 104, 112, 96, 108, 126, 112, 120, 148, 112, 128, 168, 130, 156, 160, 140, 162, 184, 160, 168, 198, 170, 192, 220, 168, 192
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,3


REFERENCES

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Sean A. Irvine, Table of n, a(n) for n = 1..10000
Donald E. Knuth and Thomas J. Buckholtz, Computation of tangent, Euler and Bernoulli numbers, Math. Comp. 21 1967 663688.
D. Shanks, Generalized Euler and class numbers, Math. Comp. 21 1967 689694.
D. Shanks, Corrigenda to: "Generalized Euler and class numbers", Math. Comp. 22 (1968), 699
D. Shanks, Generalized Euler and class numbers, Math. Comp. 21 (1967), 689694; 22 (1968), 699. [Annotated scanned copy]
Peter J. Taylor, Python program to compute terms for this and related sequences
Eric Weisstein's World of Mathematics, Tangent Number


FORMULA

From Sean A. Irvine, Mar 26 2012, corrected by Peter J. Taylor, Sep 26 2017: (Start)
Consider the Dirichlet series L_a(s) = sum_{k>=0} (a2k+1) / (2k+1)^s, where (a2k+1) is the Jacobi symbol. Then the numbers d(a,n) are defined by L_a(2n)= (pi/(2a))^(2n)*sqrt(a)* d(a,n)/ (2n1)! for a>1 and n=1,2,3...; or by L_a(2n)= (1/2)*(pi/(2a))^(2n)*sqrt(a)* d(a,n)/ (2n1)! for a=1 and n=1,2,3,...
From the Shanks paper, these can be computed as:
d(1,n)=A000182(n)
d(m^2,n)=(1/2) * m^(2n1) * (m*prod_(p_im)(p_i^(1)))^(2*n) * prod_(p_im)(p_i^(2*n)1) * d(1,n)
Otherwise write a=bm^2, b squarefree, then d(a,n)=m^(2n1) * (m*prod_(p_im)(p_i^(1)))^(2*n) * prod_(p_im)(p_i^(2*n)jacobi(b,p_i)) * d(b,n) with d(b,n), b squarefree determined by equating the recurrence
D(b,n)=sum(d(b,ni)*(b^2)^i*C(2n1,2i),i=0..n1)with the casewise expression
D(b,n)=(1)^(n1) * sum(jacobi(k,b)*(b4k)^(2n1), k=1..(b1)/2) if b == 1(mod 4)
D(b,n)=(1)^(n1) * sum(jacobi(b,2k+1)*(b(2k+1))^(2n1),2k+1<b) if b != 1(mod 4)
Sequence gives a(n)=d(n,1). (End)


PROG

(Python) See Taylor link.


CROSSREFS

Cf. A000176.
Sequence in context: A063224 A023847 A279667 * A153176 A229144 A263021
Adjacent sequences: A000058 A000059 A000060 * A000062 A000063 A000064


KEYWORD

nonn


AUTHOR

N. J. A. Sloane


EXTENSIONS

More terms from Kok Seng Chua (chuaks(AT)ihpc.nus.edu.sg), Jun 03 2000
It would be nice to have a more precise definition!  N. J. A. Sloane, May 26 2007


STATUS

approved



