A012821 Expansion of e.g.f. exp(sec(x)*arcsinh(x)).

1, 1, 1, 3, 9, 45, 225, 1071, 6993, 56697, 467745, 3279419, 29529753, 376156261, 4297350785, 35274762407, 378759492257, 8003761282417, 122599030798017, 853554115621363, 8002975063348265, 450081179390735645

Offset: 0

Author

Patrick Demichel (patrick.demichel(AT)hp.com)

Keywords

• sign

Comments

The first negative number is a(24) = -686072407102337430543.

Examples

			exp(sec(x)*arcsinh(x)) = 1 + x + 1/2!*x^2 + 3/3!*x^3 + 9/4!*x^4 + 45/5!*x^5 + ...
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 0..200

Programs

PARI

seq(n)={my(x='x+O('x^n)); Vec(serlaplace(exp(asinh(x)/cos(x))))} \\ Andrew Howroyd, Feb 25 2018