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A029851 Number of self-converse semigroups of order n. 7
1, 1, 3, 12, 64, 405, 3312, 44370, 2209839, 623492664 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..9.

Andreas Distler, Classification and Enumeration of Finite Semigroups, A Thesis Submitted for the Degree of PhD, University of St Andrews (2010).

Eric Weisstein's World of Mathematics, SemiGroup.

Index entries for sequences related to semigroups

FORMULA

a(n)=A001423(n)*2-A027851(n).

CROSSREFS

Cf. A001426.

Sequence in context: A326557 A308204 A307724 * A201720 A207557 A235129

Adjacent sequences:  A029848 A029849 A029850 * A029852 A029853 A029854

KEYWORD

nonn,hard,more,nice

AUTHOR

Christian G. Bower, Jan 27 1998. Updated Feb 19 2001

EXTENSIONS

a(8) and a(9) from Andreas Distler, Jan 17 2011

STATUS

approved

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Last modified March 28 07:59 EDT 2020. Contains 333079 sequences. (Running on oeis4.)