This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A118099 #17 Feb 16 2025 08:33:00
%S A118099 1,3,8,24,76,284,1195,5832,32254,201417,1400068,10724115,89584802,
%T A118099 809190807,7844705449
%N A118099 Number of inverse semigroups of order <= n.
%D A118099 M. V. Lawson, Inverse Semigroups: The Theory of Partial Symmetries. Singapore: World Scientific, 1999.
%D A118099 E. S. Lyapin, Semigroups. Providence, RI: Amer. Math. Soc., 1974.
%H A118099 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 A118099 Eric Weisstein et al., <a href="https://mathworld.wolfram.com/InverseSemigroup.html">Inverse Semigroup</a>.
%H A118099 <a href="/index/Se#semigroups">Index entries for sequences related to semigroups</a>.
%F A118099 a(n) = Sum_{i=1..n} A001428(i).
%e A118099 a(7) = 1195 = 1 + 2 + 5 + 16 + 52 + 208 + 911.
%Y A118099 Partial sums of A001428.
%K A118099 nonn,more
%O A118099 1,2
%A A118099 _Jonathan Vos Post_, May 11 2006
%E A118099 More terms from the data at A001428 added by _Amiram Eldar_, May 03 2023