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 A058123 Triangle read by rows: semigroups of order n with k idempotents, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator). 6
 1, 2, 2, 5, 7, 6, 19, 37, 44, 26, 132, 216, 351, 326, 135, 3107, 1780, 3093, 4157, 2961, 875, 623615, 32652, 33445, 53145, 56020, 30395, 6749, 1834861133, 4665709, 600027, 754315, 1007475, 822176, 348692, 60601, 52976551026562, 12710266442, 68769167, 14050493, 18660074, 20044250, 12889961, 4389418, 618111 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Andrey Zabolotskiy, Table of n, a(n) for n = 1..55 (rows 1-10) Andreas Distler, Classification and Enumeration of Finite Semigroups, A Thesis Submitted for the Degree of PhD, University of St Andrews (2010). Andreas Distler, Chris Jefferson, Tom Kelsey, Lars Kotthoff, The Semigroups of Order 10, in: M. Milano (Ed.), Principles and Practice of Constraint Programming, 18th International Conference, CP 2012, Québec City, QC, Canada, October 8-12, 2012, Proceedings (LNCS, volume 7514), pp. 883-899, Springer-Verlag Berlin Heidelberg 2012. A. Distler and T. Kelsey, The semigroups of order 9 and their automorphism groups, arXiv preprint arXiv:1301.6023 [math.CO], 2013. EXAMPLE Triangle starts:     1;     2,   2;     5,   7,   6;    19,  37,  44,  26;   132, 216, 351, 326, 135;   ... CROSSREFS Row sums give A001423. Main diagonal: A002788. Columns 1-3: A002786, A002787, A005591. Sequence in context: A023507 A095674 A207981 * A035586 A216392 A287908 Adjacent sequences:  A058120 A058121 A058122 * A058124 A058125 A058126 KEYWORD nonn,tabl,hard AUTHOR Christian G. Bower, Nov 10 2000 EXTENSIONS More terms from Andreas Distler, Jan 13 2011 STATUS approved

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Last modified October 23 22:10 EDT 2019. Contains 328373 sequences. (Running on oeis4.)