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%I #16 May 03 2023 09:12:39
%S 1,3,8,24,76,284,1195,5832,32254,201417,1400068,10724115,89584802,
%T 809190807,7844705449
%N Number of inverse semigroups of order <= n.
%D M. V. Lawson, Inverse Semigroups: The Theory of Partial Symmetries. Singapore: World Scientific, 1999.
%D E. S. Lyapin, Semigroups. Providence, RI: Amer. Math. Soc., 1974.
%H Alan Weinstein, <a href="https://www.ams.org/notices/199607/weinstein.pdf">Groupoids: Unifying Internal and External Symmetry</a>, Not. Amer. Math. Soc. 43, 744-752, 1996.
%H Eric Weisstein et al., <a href="http://mathworld.wolfram.com/InverseSemigroup.html">Inverse Semigroup</a>.
%H <a href="/index/Se#semigroups">Index entries for sequences related to semigroups</a>.
%F a(n) = Sum_{i=1..n} A001428(i).
%e a(7) = 1195 = 1 + 2 + 5 + 16 + 52 + 208 + 911.
%Y Partial sums of A001428.
%K nonn,more
%O 1,2
%A _Jonathan Vos Post_, May 11 2006
%E More terms from the data at A001428 added by _Amiram Eldar_, May 03 2023