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
KEYWORD
nonn,easy
AUTHOR
J. Devillet, Dec 22 2017
STATUS
approved