A046707 - OEIS

%I #12 Apr 08 2020 07:38:27

%S 1,1,6,33,472,4745,99216,1456273,39669120,769528593,25737068800,

%T 622548099041,24632715009024,715109889035737,32630102257170432,

%U 1106618435304908625,57151019891266256896,2219208490411286184737,127876294410780326952960

%N a(n) = n!*Sum_{k=0..n/2} n^(2k)/(2k)!.

%H Andrew Howroyd, <a href="/A046707/b046707.txt">Table of n, a(n) for n = 0..200</a>

%t Join[{1}, Table[(n)! Sum[n^(2 k) / (2 k)!, {k, 0, n/2}], {n, 20}]] (* _Vincenzo Librandi_, Apr 08 2020 *)

%o (PARI) a(n) = {n!*sum(k=0, n\2, n^(2*k)/(2*k)!)} \\ _Andrew Howroyd_, Mar 07 2020

%K nonn

%O 0,3

%A _N. J. A. Sloane_

%E Missing a(0)=1 inserted by _Andrew Howroyd_, Mar 07 2020