A081918 a(0) = 1; a(n) = n^(n-1)(3n-1)/2 (n>0).

1, 1, 5, 36, 352, 4375, 66096, 1176490, 24117248, 559607373, 14500000000, 414998793616, 13002646487040, 442663617327139, 16271152851709952, 642244372558593750, 27093655358260903936, 1216529796891671712025

Offset: 0

Author

Paul Barry, Mar 31 2003

Keywords

• easy
• nonn

Comments

Main diagonal of square array T(n,k) where T(n,k)=k^n(n^2-n+2k^2)/(2k^2), in which rows have g.f. (1-2kx+(k^2+1)x^2)/(1-kx)^3.

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..101

Crossrefs

Cf. A000124, A081908, A081909, A081910, A081911, A081912.

Formula

a(0)=1, a(n)=a(n)=n^n(n^2-n+2n^2)/(2n^2), n>0.