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Number of nonisomorphic and nonantiisomorphic groupoids with n elements.
(Formerly M4465 N1894)
4

%I M4465 N1894 #27 Dec 23 2021 23:02:37

%S 1,1,7,1734,89521056,1241763995193675,7162795001695681351632672,

%T 25488450150907292192918677242007992558,

%U 77841043345568973636021269757801814299054870565039692

%N Number of nonisomorphic and nonantiisomorphic groupoids with n elements.

%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%D T. Tamura, Some contributions of computation to semigroups and groupoids, pp. 229-261 of J. Leech, editor, Computational Problems in Abstract Algebra. Pergamon, Oxford, 1970.

%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 N. J. A. Sloane, <a href="/A001329/a001329.jpg">Overview of A001329, A001423-A001428, A258719, A258720.</a>

%H T. Tamura, <a href="/A001329/a001329.pdf">Some contributions of computation to semigroups and groupoids</a>, pp. 229-261 of J. Leech, editor, Computational Problems in Abstract Algebra. Pergamon, Oxford, 1970. (Annotated and scanned copy)

%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) = (A001329(n) + A029850(n))/2

%Y Cf. A001329, A029850.

%K nonn

%O 0,3

%A _N. J. A. Sloane_

%E Better description and corrected 4th term from _Christian G. Bower_, Jan 15 1998. More terms, Jun 15 1998.