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 A084409 #5 Dec 05 2013 19:56:17 %S A084409 1,3,11,9,29,18,59,28,40,54,107,69,179,87,106,125,271,147,389,172,200, %T A084409 224,541,254,286,316,346,381,727,416,941,455,495,534,575,620,1201,665, %U A084409 710,756,1493,804,1823,856,909,962,2203,1018,1077,1136,1194,1254,2621 %N A084409 Main diagonal of triangle A084408. %C A084409 a(n) is prime iff n is prime. %F A084409 For n prime, a(n) = p(A034387(n)). For n composite, a(n) = A002808([n*(n+1)/2]-A034387(n)-1). %Y A084409 Cf. A084408, A084410, A084411. %K A084409 nonn,easy %O A084409 1,2 %A A084409 _Amarnath Murthy_, Jun 01 2003 %E A084409 Edited and extended by _David Wasserman_, Dec 27 2004