A000775 a(n) = n! * (n + 1 + 2*Sum_{k=1...n} 1/k).

1, 4, 12, 46, 220, 1268, 8568, 66456, 582048, 5681952, 61174080, 720089280, 9199906560, 126783809280, 1874605662720, 29601115891200, 497155992883200, 8849184886886400, 166399076525875200, 3296032301811916800, 68596838245232640000, 1496490349337948160000

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

Links

• T. D. Noe, Table of n, a(n) for n = 0..100
• J. R. Stembridge, Some combinatorial aspects of reduced words in finite Coxeter groups, Trans. Amer. Math. Soc. 349 (1997), no. 4, 1285-1332.

Crossrefs

Similar to A000774.

Programs

Mathematica

Table[n! (n + 1 + 2*Sum[1/k, {k, n}]), {n, 0, 20}] (* T. D. Noe, Jun 20 2012 *)

Formula

E.g.f.: x/(1-x)+log(1-x)^2. - Vladeta Jovovic, Feb 02 2003

a(0)=1, a(n+1) = (n+1)*a(n) + (n+3)*n! for n > 0. - Sean A. Irvine, Jun 10 2011

Extensions

Incorrect formula deleted by Mark van Hoeij, Nov 11 2009