A275540 a(n) = n! + n!! - n - 1.

1, 0, 1, 5, 27, 129, 761, 5137, 40695, 363815, 3632629, 39927183, 479047667, 6227155921, 87178936305, 1307676395009, 20922800209903, 355687462555407, 6402373891522541, 121645101063561055, 2432902011892531179

Offset: 0

Author

Olivier Gérard, Aug 01 2016

Keywords

• nonn
• easy

Crossrefs

Cf. A006882, A110903, A128882.

Programs

Mathematica

Table[n! + n!! - n - 1, {n, 0, 20}] (* Bruno Berselli, Aug 11 2016 *)