%I #9 Dec 17 2012 14:45:07

%S 1,2,30,22456,3179460875,118459556737869096,

%T 1841479754519556293280702095,

%U 17699004125822025124951660289473617122688,146207646053305863964379580591072585873215024249550168360

%N Number of n-element groupoids with an identity, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator).

%C Also partial groupoids with n-1 elements or groupoids with an absorbant (zero) element with n elements in each case the same equivalence.

%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) = (A090601(n) + A090604(n))/2

%K nonn

%O 1,2

%A _Christian G. Bower_, Dec 05 2003