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A058133 Number of monoids (semigroups with identity) of order n, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator). 7
1, 2, 6, 27, 156, 1373, 17730, 858977, 1844075697, 52991253973742 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..10.

Eric Postpischil Posting to sci.math newsgroup, May 21 1990

Andreas Distler and Tom Kelsey, The Monoids of Order Eight and Nine. Lecture Notes in Computer Science 5144 (2008), 61-76.

Andreas Distler and Tom Kelsey, The Monoids of Orders Eight, Nine & Ten. Annals of Mathematics and Artificial Intelligence 56 (2009), 3-25.

Index entries for sequences related to monoids

FORMULA

a(n)=(A058129(n)+A058132(n))/2.

CROSSREFS

Cf. A001423, A058129, A058132, A151823.

Sequence in context: A030932 A118192 A307595 * A306857 A321584 A009308

Adjacent sequences:  A058130 A058131 A058132 * A058134 A058135 A058136

KEYWORD

nonn,more,hard

AUTHOR

Christian G. Bower, Nov 13 2000

EXTENSIONS

a(8) and a(9) from Distler & Kelsey (2008), added by N. J. A. Sloane, Jul 10 2009

a(10) from Distler & Kelsey (2009), added by Max Alekseyev, Jul 13 2009

STATUS

approved

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Last modified September 21 19:59 EDT 2019. Contains 327282 sequences. (Running on oeis4.)