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 A217919 #8 Mar 06 2013 00:31:53 %S A217919 1,3,5,8,10,16,19,20,23,51,54,58,70,71,103,136,139,142,145,153,161, %T A217919 168,169,182,204,212,219,222,224,230,232,235,240,242,276,277,286 %N A217919 Rows of A217916 in which 2's appear, when A217916 is formed into a number triangle. %C A217919 The number 2 appears only in column 1 of A217916 (when treated as a triangle). %F A217919 Involves triangular-indexed twin primes: %F A217919 prime(a(n)*(a(n)-1)/2 + 1) - prime(a(n)*(a(n)-1)/2) = 2 for n>1 with a(1)=1. %Y A217919 Cf. A217916, A217918. %K A217919 nonn %O A217919 1,2 %A A217919 _Paul D. Hanna_, Mar 04 2013