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 A001427 Number of regular semigroups of order n, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator). (Formerly M2823 N1136) 0
 1, 3, 9, 42, 206, 1352, 10168, 91073, 925044 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES 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 H. Juergensen and P. Wick, Die Halbgruppen von Ordnungen <= 7, Semigroup Forum, 14 (1977), 69-79. R. J. Plemmons, There are 15973 semigroups of order 6, Math. Algor., 2 (1967), 2-17; 3 (1968), 23. R. J. Plemmons, Cayley Tables for All Semigroups of Order Less Than 7. Department of Mathematics, Auburn Univ., 1965. S. Satoh, K. Yama, M. Tokizawa, Semigroups of order 8, Semigroup Forum 49 (1994), 7-29. N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Table of n, a(n) for n=1..9. Andreas Distler, Classification and Enumeration of Finite Semigroups, A Thesis Submitted for the Degree of PhD, University of St Andrews (2010). H. Juergensen and P. Wick, Die Halbgruppen von Ordnungen <= 7, annotated and scanned copy. R. J. Plemmons, There are 15973 semigroups of order 6 (annotated and scanned copy) N. J. A. Sloane, Overview of A001329, A001423-A001428, A258719, A258720. T. Tamura, Some contributions of computation to semigroups and groupoids, pp. 229-261 of J. Leech, editor, Computational Problems in Abstract Algebra. Pergamon, Oxford, 1970. (Annotated and scanned copy) Index entries for sequences related to semigroups CROSSREFS Sequence in context: A057724 A129879 A264521 * A020128 A018995 A018965 Adjacent sequences: A001424 A001425 A001426 * A001428 A001429 A001430 KEYWORD nonn,nice,hard,more AUTHOR N. J. A. Sloane EXTENSIONS a(8) and a(9) from Andreas Distler, Jan 17 2011 STATUS approved

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Last modified August 10 05:42 EDT 2024. Contains 375044 sequences. (Running on oeis4.)