A091912 Numerators of Taylor series for log(tan(x)+1/cos(x)).

1, 1, 1, 61, 277, 50521, 41581, 199360981, 228135437, 2404879675441, 14814847529501, 69348874393137901, 238685140977801337, 4087072509293123892361, 454540704683713199807, 441543893249023104553682821, 2088463430347521052196056349

Offset

0,4

Comments

Absolute values of (reduced) numerators of Taylor series for the Gudermannian function gd(x)= 2*arctan(exp(x))-Pi/2. - Tamas Kalmar-Nagy (integers(AT)kalmarnagy.com), Sep 28 2007

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..100

J. S. Robertson, Gudermann and the Simple Pendulum, The College Mathematics Journal, Vol. 28 (1997), No. 4, pp. 271-276.

Eric Weisstein's World of Mathematics, Gudermannian

Eric Weisstein's World of Mathematics, Inverse Gudermannian

Formula

E.g.f.: sech x or gd x. - Tamas Kalmar-Nagy (integers(AT)kalmarnagy.com), Sep 28 2007

Example

log(tan(x)+1/cos(x)) = x + 1/6*x^3 + 1/24*x^5 + 61/5040*x^7 + 277/72576*x^9 + ...
gd(x) = x - 1/6*x^3 + 1/24*x^5 - 61/5040*x^7 + 277/72576*x^9 + ....

Mathematica

Series[ArcTan[Sinh[x]], {x, 0, 30}] // CoefficientList[#, x]& // DeleteCases[#, 0]& // Numerator // Abs (* Jean-François Alcover, Feb 24 2014 *)
a[ n_] := (-1)^n Numerator @ SeriesCoefficient[ Gudermannian @ x, {x, 0, 2 n + 1}]; (* Michael Somos, Feb 24 2014 *)

Prog

(PARI) a(n)=local(X); if(n<0, 0, X=x+O(x^(2*n+2)); numerator(polcoeff(log(tan(X)+1/cos(X)), 2*n+1)))

Crossrefs

Cf. A000364, A028296.

Sequence in context: A252803 A302282 A140854 * A142605 A142133 A302730

Adjacent sequences: A091909 A091910 A091911 * A091913 A091914 A091915

Keyword

nonn,frac,easy

Author

Michael Somos, Feb 12 2004

Extensions

More terms from Vincenzo Librandi, Feb 26 2014

Status

approved