OFFSET
-1,2
REFERENCES
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, Tenth Printing, 1972, p. 75 (4.3.70).
G. W. Caunt, Infinitesimal Calculus, Oxford Univ. Press, 1914, p. 477.
L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 88.
H. Rademacher, Topics in Analytic Number Theory, Springer, 1973, Chap. 1, p. 19.
LINKS
Seiichi Manyama, Table of n, a(n) for n = -1..250 (terms -1..100 from T. D. Noe)
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, Tenth Printing, 1972, p. 75 (4.3.70).
Eric Weisstein's World of Mathematics, Cotangent
FORMULA
cot(x) = Sum_{k>=0} (-1)^k B_{2k} 4^k x^(2k-1) / (2k)!.
a(n) = denominator(A000182(n)/(4^n-1)), n>0.
a(n) = denominator for coth x;
coth(x) = W(0)/x -1, W(k) = k+1+2*x-2*x*(k+1)/W(k+1); (continued fraction). - Sergei N. Gladkovskii, Nov 27 2011
coth(x) = Q(0)/(1+x)/x^2 - 1 where Q(k) = 2*k^3 + (2*x+3)*k^2 + (2*x^2+3*x+1)*k + 2*x^3 + 2*x^2 + x - 2*x^2*(k+1)*(2*k+1)*(x+k)*(x+k+2)/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, Feb 28 2013
a(n) = denominator of 4^(n+1)*Zeta(-2*n-1)/(2*n+1)! for n >= 0. - Peter Luschny, Jun 20 2013
a(n) = denominator(r(n)), with the negative rational numbers r(n) = [x^n]( (cot(sqrt(x))-1/sqrt(x))/sqrt(x)) for n >= 0. - Wolfdieter Lang, Oct 07 2016
EXAMPLE
G.f. = 1/x - (1/3)*x - (1/45)*x^3 - (2/945)*x^5 - (1/4725)*x^7 - (2/93555)*x^9 + O(x^11).
MAPLE
A036278 := n -> `if`(n<0, 1, denom(4^(n+1)*Zeta(-2*n-1)/(2*n+1)!));
seq(A036278(n), n = -1..20); # Peter Luschny, Jun 20 2013
MATHEMATICA
Denominator[Select[List@@Series[Cot[x], {x, 0, 20}][[3]], #!=0&]] (* Harvey P. Dale, Apr 11 2011 *)
a[n_] := (-1)^(n+1)*4^(n+1)*BernoulliB[2*n+2]/(2*n+2)! // Denominator; Table[a[n], {n, -1, 20}] (* Jean-François Alcover, Apr 14 2014, after Peter Luschny *)
PROG
(PARI) apply(r->denominator(r), Vec(1/tan(x))) \\ Charles R Greathouse IV, Apr 14 2014
(PARI) a(n) = denominator((-1)^(n+1)*4^(n+1)*bernfrac(2*n+2)/(2*n+2)!); \\ Altug Alkan, Dec 02 2015
(Python)
from sympy import bernoulli, factorial
def a(n):
return ((-4)**(n + 1)*bernoulli(2*n + 2)/factorial(2*n + 2)).denominator()
print([a(n) for n in range(-1, 20)]) # Indranil Ghosh, Jun 23 2017
(Magma) [Denominator((-1)^(n+1)*4^(n+1)*Bernoulli(2*n+2)/Factorial(2*n+2) ): n in [-1..20]]; // G. C. Greubel, Jul 03 2019
(Sage) [denominator( (-1)^(n+1)*4^(n+1)*bernoulli(2*n+2)/factorial(2*n+2) ) for n in (-1..20)] # G. C. Greubel, Jul 03 2019
(GAP) List([-1..20], n-> DenominatorRat( (-1)^(n+1)*4^(n+1)* Bernoulli(2*n+2)/Factorial(2*n+2) )) # G. C. Greubel, Jul 03 2019
CROSSREFS
KEYWORD
nonn,frac,easy,nice
AUTHOR
STATUS
approved