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 A138881 #2 Mar 30 2012 17:33:54 %S A138881 1,1,3,1,2,3,6,1,2,5,10,1,3,5,15,1,3,7,21,1,2,4,7,14,28,1,2,3,4,6,9, %T A138881 12,18,36,1,3,5,9,15,45,1,5,11,55,1,2,3,6,11,22,33,66,1,2,3,6,13,26, %U A138881 39,78,1,7,13,91,1,3,5,7,15,21,35,105 %N A138881 Array read by rows: row n lists divisors of n-th positive triangular number A000217(n). %e A138881 Array begins: %e A138881 1 %e A138881 1, 3 %e A138881 1, 2, 3, 6 %e A138881 1, 2, 5, 10 %e A138881 1, 3, 5, 15 %e A138881 1, 3, 7, 21 %e A138881 1, 2, 4, 7, 14, 28 %Y A138881 Cf. A000217, A133021, A133031, A138882. %K A138881 easy,nonn,tabf %O A138881 1,3 %A A138881 _Omar E. Pol_, Apr 11 2008