A046673 a(n) = (2n)!*Sum_{i=1..n} 1/i.

2, 36, 1320, 84000, 8285760, 1173553920, 226040855040, 56865153945600, 18112111963545600, 7125892746964992000, 3394344333441245184000, 1925382105537337294848000, 1282520788685931213619200000, 991363455147400701817651200000, 880169729965718014490443776000000

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Links

• I. Nemes et al., How to do Monthly problems with your computer, Amer. Math. Monthly, 104 (1997), 505-519.

Crossrefs

Cf. A000254, A101613.

Programs

Mathematica

Table[(2n)!HarmonicNumber[n],{n,20}] (* Harvey P. Dale, Sep 27 2013 *)

PARI

a(n) = (2*n)!*sum(k=1, n, 1/k); \\ Michel Marcus, Jul 11 2018