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A079201 Number of isomorphism classes of associative commutative closed binary operations on a set of order n, listed by class size. 5
1, 0, 3, 0, 0, 3, 9, 0, 0, 0, 3, 0, 0, 16, 39 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

A079194(n)+A079197(n)+A079200(n)+A079201(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; 0,3; 0,0,3,9; 0,0,0,3,0,0,16,39

A023815(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 x of this sequence is given by A001426(x).

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. A001426, A023815, A079194, A079197, A079200. a(n, A027423(n)) = A058105(n).

Sequence in context: A151665 A171793 * A079209 A279368 A021773 A244126

Adjacent sequences:  A079198 A079199 A079200 * A079202 A079203 A079204

KEYWORD

nonn,tabf

AUTHOR

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

STATUS

approved

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Last modified October 16 00:50 EDT 2018. Contains 316252 sequences. (Running on oeis4.)