A296944 Expansion of (2*x*exp(x)-3)/(1-x).

0, 1, 2, 12, 56, 290, 1752, 12278, 98240, 884178, 8841800, 97259822, 1167117888, 15172532570, 212415456008, 3186231840150, 50979709442432, 866655060521378, 15599791089384840, 296396030698311998, 5927920613966240000, 124486332893291040042

Offset

0,3

Comments

Number of bisymmetric and quasitrivial binary operations on {1,...,n} that have annihilator elements.

Links

Robert G. Wilson v, Table of n, a(n) for n = 0..449

J. Devillet, Bisymmetric and quasitrivial operations: characterizations and enumerations, arXiv:1712.07856 [math.RA] (2017).

Formula

a(n) = A296943(n)-2, a(0) = 0, a(1) = 1.

Mathematica

Join[{0, 1}, Delete[ Range[0, 21]! CoefficientList[ Series[(2x*Exp[x] -3)/(1 -x), {x, 0, 21}], x], {{1}, {2}}]] (* Robert G. Wilson v, Dec 22 2017 *)

Crossrefs

Cf. A296943.

Sequence in context: A078543 A084128 A044047 * A105487 A098453 A256150

Adjacent sequences: A296941 A296942 A296943 * A296945 A296946 A296947

Keyword

nonn,easy

Author

J. Devillet, Dec 22 2017

Status

approved