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 A217920 #6 Mar 06 2013 00:33:31 %S A217920 2,1,2,4,2,6,6,2,6,2,6,14,4,12,6,2,4,4,2,2,6,6,2,4,6,8,6,16,6,4,6,6,6, %T A217920 6,6,6,14,6,6,14,10,10,8,4,12,20,8,12,6,10,2,6,14,2,14,18,6,2,6,12,4, %U A217920 28,6,20,6,6,6,4,16,2,2,6,4,12,6,6,6,6,8,4,6,8,6 %N A217920 Column 1 of A217916 (when formed into a number triangle). %C A217920 The number 2 appears in A217916 only in column 1. %C A217920 The positions of 2 are given by A217919. %H A217920 Paul D. Hanna, <a href="/A217920/b217920.txt">Table of n, a(n) for n = 1..287</a> %F A217920 a(n) = prime(n*(n-1)/2 + 1) - prime(n*(n-1)/2) for n>1 with a(1)=2. %Y A217920 Cf. A217916, A217918, A217919. %K A217920 nonn %O A217920 1,1 %A A217920 _Paul D. Hanna_, Mar 04 2013