A278565 a(n) = Sum_{t=1..n} binomial(n,t)*t^(1+(n-t)^2).

0, 1, 4, 18, 236, 12760, 3162582, 5965957900, 147395915019656, 38431930179989653632, 90116582088416163834417290, 2118032070086776060232851050813004, 966490912699216393489571072350268614425420, 17165261065730992639912668446254005264689353839299152

Offset

0,3

Links

Table of n, a(n) for n=0..13.

Daniel J. Kleitman, Bruce L. Rothschild and Joel H. Spencer, The number of semigroups of order n, Proc. Amer. Math. Soc., 55 (1976), 227-232. See Eq. (1.2).

Mathematica

Table[Sum[Binomial[n, t]  t^(1 + (n - t)^2), {t, 1, n}], {n, 0, 25}] (* Vincenzo Librandi, Nov 27 2016 *)

Crossrefs

Cf. A001423.

Sequence in context: A143993 A145660 A246531 * A370189 A360283 A214168

Adjacent sequences: A278562 A278563 A278564 * A278566 A278567 A278568

Keyword

nonn

Author

N. J. A. Sloane, Nov 25 2016

Status

approved