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A101928 E.g.f. cos(arcsinh(x)) = sin(arccosh(x)) (even powers only). 5
1, -1, 5, -85, 3145, -204425, 20646925, -2993804125, 589779412625, -151573309044625, 49261325439503125, -19753791501240753125, 9580588878101765265625, -5527999782664718558265625, 3742455852864014463945828125, -2937827844498251354197475078125, 2646982887892924470131925045390625 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Absolute values are expansion of e.g.f. cosh(arcsin(x)).
LINKS
FORMULA
E.g.f.: cos(arcsinh(x)) = sqrt(1+x^2)*(1-x^2*(1-5*x^2/(G(0)+5*x^2))); G(k) = (k+2)*(2*k+3)-x^2*(2*k^2+6*k+5)+x^2*(k+2)*(2*k+3)*(2*k^2+10*k+13)/G(k+1);
For cosh(arcsin(x)) = sqrt(1-x^2)*(1 + x^2*(1 + 5*x^2/(G(0) - 5*x^2))); G(k) = x^2*(2*k^2+6*k+5) + (k+2)*(2*k+3) - x^2*(k+2)*(2*k+3)*(2*k^2+10*k+13)/G(k+1); (continued fraction). - Sergei N. Gladkovskii, Dec 19 2011
G.f.: 1 - x*(1 + x*(G(0) - 1)/(x-1)) where G(k) = 1 + ((2*k+2)^2+1)/(1-x/(x - 1/G(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Jan 15 2013
a(n) ~ (-1)^(n+1) * sinh(Pi/2) * 2^(2*n-2) * n^(2*n-3) / exp(2*n). - Vaclav Kotesovec, Oct 23 2013
For n>1, a(n) = (-1)^(n+1) * A277354(n-2). - Vaclav Kotesovec, Oct 10 2016
EXAMPLE
cos(arcsinh(x)) = 1 - x^2/2 + 5x^4/4! - 85x^6/6! + 3145x^8/8! - ...
MAPLE
seq(coeff(series(factorial(n)*cos(arcsinh(x)), x, n+1), x, n), n=0..40, 2); # Muniru A Asiru, Jul 22 2018
MATHEMATICA
Table[n!*SeriesCoefficient[Cos[ArcSinh[x]], {x, 0, n}], {n, 0, 40, 2}] (* Vaclav Kotesovec, Oct 23 2013 *)
Flatten[{1, Table[(-1)^(n+1)*Product[4*k^2 + 1, {k, 1, n}], {n, 0, 12}]}] (* Vaclav Kotesovec, Oct 10 2016 *)
CROSSREFS
Bisection of A006228.
Sequence in context: A318635 A203800 A277354 * A012788 A208886 A192055
KEYWORD
sign
AUTHOR
Ralf Stephan, Dec 28 2004
STATUS
approved

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Last modified February 26 22:44 EST 2024. Contains 370354 sequences. (Running on oeis4.)