A055865 Second column of triangle A055864.

0, 2, 12, 100, 1080, 14406, 229376, 4251528, 90000000, 2143588810, 56757583872, 1654301902188, 52644347205632, 1816448730468750, 67553994410557440, 2694045224950414864, 114692890480116793344, 5191945444217181018258, 249036800000000000000000, 12617615847934310595791220

Offset

1,2

Links

Paolo Xausa, Table of n, a(n) for n = 1..350

Milan Janjić, Enumerative Formulas for Some Functions on Finite Sets.

Formula

a(n) = A055864(n, 2).

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

E.g.f.: -1/2*(-W(-x)^2 + x^2)/x, W(x) principal branch of Lambert's function.

a(n) ~ exp(1-5/(2*n)) * n^(n-1). - Amiram Eldar, Feb 07 2026

Mathematica

A055865[n_] := If[n == 1, 0, n*(n+1)^(n-2)];
Array[A055865, 25] (* Paolo Xausa, Aug 07 2025 *)

Crossrefs

Cf. A055864, A000272, A055858.

Sequence in context: A303614 A124102 A168365 * A085389 A202013 A151505

Adjacent sequences: A055862 A055863 A055864 * A055866 A055867 A055868

Keyword

nonn,easy

Author

Wolfdieter Lang, Jun 20 2000

Status

approved