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Number of anti-associative closed binary operations on a set of order n.
5

%I #18 Sep 03 2024 08:24:54

%S 1,0,2,52,421560

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

%H Christian 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 a(n) = A002489(n) - A079176(n).

%F a(n) = Sum_{k>=1} A079181(n,k)*A079210(n,k).

%Y Cf. A079176, A079180 (isomorphism classes), A079181, A079210.

%K nonn,more

%O 0,3

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

%E a(0)=1 prepended and a(1) corrected by _Kamil Zabielski_, Aug 28 2024