A329063 a(n) = a(n-1)! + a(n-1) with a(1)=1.

1, 2, 4, 28, 304888344611713860501504000028

Offset: 1

Author

Ananthakrishna Kaithalayil, Nov 02 2019

Keywords

• nonn

Comments

The next term is too large to include, since it has about 8.85695956*10^30 digits.

No term can be represented by a sum of three positive squares, because a(4) and the following terms can all be written as 4*(8*k+7) for k>=0.

Examples

			a(3) = a(3-1)! + a(3-1) = a(2)! + a(2) = 4.
		

Crossrefs

Cf. A000408 (sums of 3 squares).

Programs

Mathematica

a[1]=1; a[n_] := a[n-1]! + a[n-1]; Array[a, 5] (* Giovanni Resta, Nov 03 2019 *)

Formula

a(n) = a(n-1)! + a(n-1)

Extensions

Edited by N. J. A. Sloane, Nov 03 2019