A012254 exp(arcsinh(arctanh(x)))=1+x+1/2!*x^2+2/3!*x^3+5/4!*x^4+24/5!*x^5...

1, 1, 1, 2, 5, 24, 109, 720, 4521, 40320, 330681, 3628800, 36468717, 479001600, 5721101541, 87178291200, 1205289090513, 20922789888000, 328897528901361, 6402373705728000, 112769846051251797, 2432902008176640000

Offset: 0

Author

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

Keywords

• nonn

Crossrefs

Bisections are A010050 and |A012091|.

Formula

E.g.f.: Q(0)-1, where Q(k) = 2 + arctanh(x)/(1 - arctanh(x)/Q(k+1) ); (continued fraction). - Sergei N. Gladkovskii, Dec 19 2013