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 A100253 #2 Mar 30 2012 17:23:21 %S A100253 8,3,241,97,26,49,8,0,55,31,23,97,274,15,721,49,120,0,305,161,1681,89, %T A100253 24,577,1126,53,244,3361,146,241,528,97,991,35,351,6049,223,191,65521, %U A100253 1921,288,127,213281,485,10081,323,48,721,1520,0,2449 %N A100253 Let j be the smallest integer for which 1+(1+1*n)+(1+2*n)+...+(1+j*n)=k^2=s. Then a(n)=1+j*n; if no such j exists, then a(n)=0. %C A100253 Basis for sequence is shortest arithmetic series with initial term 1 and difference n that sums to a perfect square. %F A100253 1+(1+1*n)+(1+2*n)+...+(1+A100254(n)*n)= 1+(1+1*n)+(1+2*n)+...+a(n)=A100251(n)^2=A100252(n) %e A100253 a(3)=241 since 1 + 4 + 7 +...+ 241 = 99^2 = 9801 and no other arithmetic series with initial term 1, difference 3 and fewer terms sums to a perfect square. %K A100253 nonn %O A100253 1,1 %A A100253 _Charlie Marion_, Nov 21 2004