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A079175 Number of isomorphism classes of associative closed binary operations (semigroups) on a set of order n, listed by class size. 3
1, 2, 3, 2, 0, 7, 15, 2, 0, 0, 7, 5, 0, 62, 112 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A079174(n)+A079175(n)=A079171(n)

Elements per row: 1,2,4,8,16,30,... (given by A027423, number of positive divisors of n!)

First four rows: 1; 2,3; 2,0,7,15; 2,0,0,7,5,0,62,112

A023814(x) is equal to the sum of the products of each element in row x of this sequence and the corresponding element of A079210.

The sum of each row n is given by A027851(n).

LINKS

Table of n, a(n) for n=1..15.

C. van den Bosch, Closed binary operations on small sets

Index entries for sequences related to semigroups

CROSSREFS

Cf. A023814, A027851, A079174. a(n, A027423(n)) = A058104(n).

Sequence in context: A011024 A105855 A152954 * A202815 A049336 A017888

Adjacent sequences:  A079172 A079173 A079174 * A079176 A079177 A079178

KEYWORD

nonn,tabf

AUTHOR

Christian van den Bosch (cjb(AT)cjb.ie), Jan 03 2003

STATUS

approved

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Last modified February 24 07:50 EST 2018. Contains 299599 sequences. (Running on oeis4.)