cp's OEIS Frontend

A001427 Number of regular semigroups of order n, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator).

%I A001427 M2823 N1136 #35 Aug 15 2025 04:43:29
%S A001427 1,3,9,42,206,1352,10168,91073,925044
%N A001427 Number of regular semigroups of order n, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator).
%D A001427 Tak-Shing T. Chan, YH Yang, Polar n-Complex and n-Bicomplex Singular Value Decomposition and Principal Component Pursuit, IEEE Transactions on Signal Processing ( Volume: 64, Issue: 24, Dec.15, 15 2016 ); DOI: 10.1109/TSP.2016.2612171
%D A001427 R. J. Plemmons, There are 15973 semigroups of order 6, Math. Algor., 2 (1967), 2-17; 3 (1968), 23.
%D A001427 R. J. Plemmons, Cayley Tables for All Semigroups of Order Less Than 7. Department of Mathematics, Auburn Univ., 1965.
%D A001427 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A001427 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A001427 Andreas Distler, <a href="http://hdl.handle.net/10023/945">Classification and Enumeration of Finite Semigroups</a>, A Thesis Submitted for the Degree of PhD, University of St Andrews (2010).
%H A001427 H. Juergensen and P. Wick, <a href="https://gdz.sub.uni-goettingen.de/id/PPN362162808_0014">Die Halbgruppen von Ordnungen <= 7</a>, Semigroup Forum, 14 (1977), 69-79.
%H A001427 H. Juergensen and P. Wick, <a href="/A001423/a001423.pdf">Die Halbgruppen von Ordnungen <= 7</a>, annotated and scanned copy.
%H A001427 R. J. Plemmons, <a href="/A001423/a001423_2.pdf">There are 15973 semigroups of order 6</a> (annotated and scanned copy)
%H A001427 S. Satoh, K. Yama, M. Tokizawa, <a href="https://gdz.sub.uni-goettingen.de/id/PPN362162808_0049">Semigroups of order 8</a>, Semigroup Forum 49 (1994), 7-29.
%H A001427 N. J. A. Sloane, <a href="/A001329/a001329.jpg">Overview of A001329, A001423-A001428, A258719, A258720.</a>
%H A001427 T. Tamura, <a href="/A001329/a001329.pdf">Some contributions of computation to semigroups and groupoids</a>, pp. 229-261 of J. Leech, editor, Computational Problems in Abstract Algebra. Pergamon, Oxford, 1970. (Annotated and scanned copy)
%H A001427 <a href="/index/Se#semigroups">Index entries for sequences related to semigroups</a>
%K A001427 nonn,nice,hard,more
%O A001427 1,2
%A A001427 _N. J. A. Sloane_
%E A001427 a(8) and a(9) from _Andreas Distler_, Jan 17 2011