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Number of non-associative commutative closed binary operations on a set of order n.
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%I #10 Jan 26 2022 23:09:05

%S 0,0,2,666,1047436,30517547395,21936950639192784,

%T 459986536544739894613595,324518553658426726783148869733112

%N Number of non-associative commutative closed binary operations on a set of order n.

%H C. van den Bosch, <a href="https://web.archive.org/web/20071014230143/http://cosmos.ucc.ie/~cjvdb1/html/binops.shtml">Closed binary operations on small sets</a>

%H <a href="/index/Gre#groupoids">Index entries for sequences related to groupoids</a>

%F A079192(n) + a(n) + A079198(n) + A023815(n) = A002489(n).

%F a(n) = Sum_{k>=1} A079197(n,k)*A079210(n,k).

%F a(n) = A023813(n) - A023815(n). - _Andrew Howroyd_, Jan 26 2022

%Y Cf. A023813, A023815, A079192, A079196 (isomorphism classes), A079197, A079198.

%K nonn

%O 0,3

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

%E a(0)=0 prepended and a(5)-a(8) added by _Andrew Howroyd_, Jan 26 2022