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A329063
a(n) = a(n-1)! + a(n-1) with a(1)=1.
0
1, 2, 4, 28, 304888344611713860501504000028
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
Cf. A000408 (sums of 3 squares).
Sequence in context: A248872 A329102 A126580 * A124687 A267122 A018291
KEYWORD
nonn
AUTHOR
_Ananthakrishna Kaithalayil_, Nov 02 2019
EXTENSIONS
Edited by N. J. A. Sloane, Nov 03 2019
STATUS
approved