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 A171099 #19 Jun 27 2022 23:49:09 %S A171099 1,1,1,2,1,2,0,1,1,1,2,0,0,1,0,2,1,2,0,0,0,2,0,0,2,0,0,8,1,2,0,0,4,4, %T A171099 16,0,0,0,0,0,0,0,2,0,0,0,0,0,0,16,0,0,0,0,1,0,0,0,0,32,0,0,0,0,0,0,2, %U A171099 0,16,0,0,0,2,0,0,0,0,0,0,16,2,4,0,0,0,2,1,0,0,0,0,0,0 %N A171099 a(n) = number of solutions (x,y) (with 0 <= x <= y) to x*(x+1)/2 + y*(y+1)/2 = n!. %F A171099 a(n) = A000161(8*n! + 2). - _Max Alekseyev_, Dec 12 2011 %e A171099 Initial solutions: (x,y,n) = (0,1,0), (0,1,1), (1,1,2), (0,3,3), (2,2,3), (2,6,4), (0,15,5), (5,14,5), (45,89,7), (89,269,8), (210,825,9), (760,2610,10), (1770,2030,10), none for n = 11 or 12, one for n = 13 (71504,85680,13) (found by _Ed Pegg Jr_), etc. %Y A171099 Cf. A000161, A152089 (n for which no solutions exist), A180590 (n for which solutions exist). %K A171099 nonn %O A171099 0,4 %A A171099 _N. J. A. Sloane_, Sep 24 2010, based on a posting by _R. K. Guy_ to the Sequence Fans Mailing List, Sep 10 2010 %E A171099 Corrected and extended (with data from _Georgi Guninski_, at the suggestion of _N. J. A. Sloane_) by _D. S. McNeil_, Sep 26 2010