OFFSET
0,3
LINKS
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
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 25 2016
STATUS
approved