OFFSET
1,3
FORMULA
For even n, a(n) = n!^2 / (2n). For odd n, a(n) = (n!^2 + n!) / (2n).
a(1) = 1; For n > 1: a(n) = Sum_{j=0..n-1} (abs((n - 1)! - n!*Stirling1(n - 1, j)))/2. - Detlef Meya, Apr 10, 2024
MATHEMATICA
a[1]=1; a[n_]:=Sum[Abs[(n-1)!-n!*StirlingS1[n-1, j]], {j, 0, n-1}]/2; Flatten[Table[a[n], {n, 1, 18}]] (* Detlef Meya, Apr 10, 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Max Alekseyev, Feb 09, 2008
STATUS
approved