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 A164561 #4 Mar 31 2012 08:58:36 %S A164561 1,1,1,1,4,1,1,1,1,1,1,16,27,4,1,1,1,1,1,1,1,1,4,1,16,1,4,1,1,1,9,1,1, %T A164561 9,1,1,1,16,1,4,25,16,1,4,1,1,1,1,1,1,1,1,1,1,1,1,4,27,128,1,108,1,16, %U A164561 9,4,1,1,1,1,1,1,1,1,1,1,1,1,1,1,16,1,4,1,16,49,4,1,16,1,4,1,1,1,27,1 %N A164561 Triangle with elements A120070(m,n)/A120072(m,n) read by rows, m>=2, 1<=n<m. %e A164561 The triangle starts in row m=2 as %e A164561 1; %e A164561 1, 1; %e A164561 1, 4, 1; %e A164561 1, 1, 1, 1; %e A164561 1, 16, 27, 4, 1; %e A164561 1, 1, 1, 1, 1, 1; %e A164561 1, 4, 1, 16, 1, 4, 1; %p A164561 A120070 := proc(m,n) m^2-n^2 ; end: A120072 := proc(m,n) numer(1/n^2-1/m^2) ; end: %p A164561 A164561 := proc(m,n) A120070(m,n)/A120072(m,n) ; end: seq( seq(A164561(m,n),n=1..m-1), m=2..30) ; # _R. J. Mathar_, Aug 19 2009 %K A164561 nonn,tabl,easy %O A164561 2,5 %A A164561 _Paul Curtz_, Aug 16 2009 %E A164561 Edited and extended by _R. J. Mathar_, Aug 19 2009