OFFSET
1,2
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.
FORMULA
a(n) = a(n-1)! + a(n-1)
EXAMPLE
a(3) = a(3-1)! + a(3-1) = a(2)! + a(2) = 4.
MATHEMATICA
a[1]=1; a[n_] := a[n-1]! + a[n-1]; Array[a, 5] (* Giovanni Resta, Nov 03 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
_Ananthakrishna Kaithalayil_, Nov 02 2019
EXTENSIONS
Edited by N. J. A. Sloane, Nov 03 2019
STATUS
approved