1,2

M. V. Lawson, Inverse Semigroups: The Theory of Partial Symmetries. Singapore: World Scientific, 1999.

E. S. Lyapin, Semigroups. Providence, RI: Amer. Math. Soc., 1974.

Weinstein, A. "Groupoids: Unifying Internal and External Symmetry." Not. Amer. Math. Soc. 43, 744-752, 1996.

Eric Weisstein et al., Inverse Semigroup.

Index entries for sequences related to semigroups.

a(n) = SUM[i=1..n] A001428(i).

a(7) = 1195 = 1 + 2 + 5 + 16 + 52 + 208 + 911.

Partial sums of A001428.

Sequence in context: A046342 A000958 A084205 this_sequence A066350 A088966 A125655

Adjacent sequences: A118096 A118097 A118098 this_sequence A118100 A118101 A118102

nonn

Jonathan Vos Post (jvospost2(AT)yahoo.com), May 11 2006