This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A258720 #10 May 06 2023 17:24:03 %S A258720 0,3,1596,89460896,1241763541901150,7162795001623210170643008, %T A258720 25488450150907291894372809845206177481, %U A258720 77841043345568973636021232493841647618443964915982324,270925719901279918478856582434909122129159229348142178651137261056627814 %N A258720 Number of non-self-dual groupoids which are equal to their duals. %H A258720 N. J. A. Sloane, <a href="/A001329/a001329.jpg">Overview of A001329, A001423-A001428, A258719, A258720.</a> %H A258720 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) %F A258720 a(n) = (A001329(n) - A029850(n))/2. - _Andrew Howroyd_, May 06 2023 %Y A258720 Cf. A001329, A001424, A029850, A258719. %K A258720 nonn %O A258720 1,2 %A A258720 _N. J. A. Sloane_, Jun 18 2015 %E A258720 Terms a(5) and beyond from _Andrew Howroyd_, May 06 2023