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A036278
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Denominators in Taylor series for cot x.
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4
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1, 3, 45, 945, 4725, 93555, 638512875, 18243225, 162820783125, 38979295480125, 1531329465290625, 13447856940643125, 201919571963756521875, 11094481976030578125, 564653660170076273671875, 5660878804669082674070015625, 31245110285511170603633203125
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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-1,2
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REFERENCES
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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.
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LINKS
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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
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FORMULA
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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) same 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
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EXAMPLE
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x^(-1)-1/3*x-1/45*x^3-2/945*x^5-1/4725*x^7-2/93555*x^9+O(x^11).
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MAPLE
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A036278 := n -> `if`(n<0, 1, denom(4^(n+1)*Zeta(-2*n-1)/(2*n+1)!));
seq(A036278(n), n = -1..15); # Peter Luschny, Jun 20 2013
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MATHEMATICA
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Denominator[Select[List@@Series[Cot[x], {x, 0, 40}][[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, 15}] (* Jean-François Alcover, Apr 14 2014, after Peter Luschny *)
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PROG
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(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
from fractions import Fraction
def a(n): return Fraction(str((-1)**(n + 1)*4**(n + 1)*bernoulli(2*n + 2)/factorial(2*n + 2))).denominator
print [a(n) for n in xrange(-1, 101)] # Indranil Ghosh, Jun 23 2017
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CROSSREFS
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Cf. A000182, A002431 (numerators).
Sequence in context: A298799 A202437 A008931 * A225149 A154289 A171080
Adjacent sequences: A036275 A036276 A036277 * A036279 A036280 A036281
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KEYWORD
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nonn,frac,easy,nice
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AUTHOR
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N. J. A. Sloane
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STATUS
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approved
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