A109779 - OEIS

A109779

a(n) = n! * Sum_{k=1..n} H(k)*(n+1-k)!, where H(k) = Sum_{j=1..k} 1/j.

1, 7, 65, 930, 20814, 693732, 32312412, 1996944912, 157655618928, 15457109916960, 1841080739130720, 261722785741833600, 43758563047332750720, 8498963447183108148480, 1897379318289205012550400, 482444035336741492040140800, 138599348510645114991010560000

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OFFSET

1,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..200

FORMULA

E.g.f.: (hypergeom([1, 1], [], x)+x*hypergeom([2, 2], [], x))*log(1-x)/(x-1). - Vladeta Jovovic, Aug 17 2005

MATHEMATICA

a[n_] := n! * Sum[(n+1-k)! * Sum[1/j, {j, 1, k}], {k, 1, n}]; Table[a[n], {n, 1, 30}] (* Ryan Propper, Sep 01 2005 *)

PROG

(PARI) a(n) = n!*sum(k=1, n, sum(j=1, k, 1/j)*(n+1-k)!); \\ Michel Marcus, Nov 20 2018

CROSSREFS