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Number of n-element labeled commutative groupoids with an identity.
1

%I #10 Jan 11 2013 16:22:16

%S 1,4,81,16384,48828125,2821109907456,3909821048582988049,

%T 154742504910672534362390528,202755595904452569706561330872953769,

%U 10000000000000000000000000000000000000000000000

%N Number of n-element labeled commutative groupoids with an identity.

%C Also labeled commutative groupoids with an absorbant (zero) element.

%H Eric Postpischil <a href="http://groups.google.com/groups?&amp;hl=en&amp;lr=&amp;ie=UTF-8&amp;selm=11802%40shlump.nac.dec.com&amp;rnum=2">Posting to sci.math newsgroup, May 21 1990</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Groupoid.html">Groupoid.</a>

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

%F a(n) = n^(1+binomial(n, 2))

%Y a(n) = A076113(n)*n. Cf. A038017.

%K nonn

%O 1,2

%A _Christian G. Bower_, Dec 05 2003