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A079171 Number of isomorphism classes of closed binary operations (groupoids) on a set of order n, listed by class size. 20
1, 4, 6, 3, 12, 78, 3237, 2, 1, 14, 30, 275, 495, 48810, 178932325 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

First four rows: 1; 4,6; 3,12,78,3237; 2,1,14,30,275,495,48810,178932325

A002489(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 is given by A001329(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 groupoids

CROSSREFS

Cf. A002489, A001329. a(n, A027423(n)) = A030245(n).

Sequence in context: A082193 A255767 A274926 * A029678 A123732 A244339

Adjacent sequences:  A079168 A079169 A079170 * A079172 A079173 A079174

KEYWORD

nonn,tabf

AUTHOR

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

STATUS

approved

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Last modified May 20 20:16 EDT 2019. Contains 323426 sequences. (Running on oeis4.)