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 A079171 #8 Aug 03 2025 17:08:57 %S A079171 1,4,6,3,12,78,3237,2,1,14,30,275,495,48810,178932325 %N A079171 Number of isomorphism classes of closed binary operations (groupoids) on a set of order n, listed by class size. %C A079171 Elements per row: 1,2,4,8,16,30,... (given by A027423, number of positive divisors of n!) %C A079171 A002489(n) is equal to the sum of the products of each element in row n of this sequence and the corresponding element of A079210. %C A079171 The sum of each row n is given by A001329(n). %H A079171 C. van den Bosch, <a href="http://cosmos.ucc.ie/~cjvdb1/html/binops.shtml">Closed binary operations on small sets</a> %H A079171 <a href="/index/Gre#groupoids">Index entries for sequences related to groupoids</a> %e A079171 First four rows: %e A079171 1; %e A079171 4, 6; %e A079171 3, 12, 78, 3237; %e A079171 2, 1, 14, 30, 275, 495, 48810, 178932325. %Y A079171 Cf. A002489, A001329. a(n, A027423(n)) = A030245(n). %K A079171 nonn,tabf %O A079171 1,2 %A A079171 Christian van den Bosch (cjb(AT)cjb.ie), Jan 03 2003