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 A139597 #11 Jun 17 2017 04:00:46 %S A139597 0,7,15,30,46,69,93,124,156,195,235,282,330,385,441,504,568,639,711, %T A139597 790,870,957,1045,1140,1236,1339,1443,1554,1666,1785,1905,2032,2160, %U A139597 2295,2431,2574,2718,2869,3021,3180,3340,3507,3675,3850 %N A139597 A139278(n) followed by A139274(n+1). %C A139597 Sequence found by reading the line from 0, in the direction 0, 7,... and the line from 15, in the direction 15, 46,..., in the square spiral whose vertices are the triangular numbers A000217. %H A139597 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %H A139597 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1). %F A139597 Array read by rows: row n gives 8*n^2 + 7n, 8*(n+1)^2 - (n+1). %F A139597 a(n) = (3-3*(-1)^n+14*n+8*n^2)/4. a(n) = 2*a(n-1)-2*a(n-3)+a(n-4). G.f.: x*(7+x)/((1-x)^3*(1+x)). [_Colin Barker_, Jul 22 2012] %e A139597 Array begins: %e A139597 0, 7 %e A139597 15, 30 %e A139597 46, 69 %e A139597 93, 124 %Y A139597 Cf. A000217, A046092, A139274, A139278, A077221, A139591, A139592, A139593, A139595, A139596, A139598. %K A139597 easy,nonn %O A139597 0,2 %A A139597 _Omar E. Pol_, May 03 2008