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 A139592 #11 Jun 17 2017 04:00:46 %S A139592 0,2,10,20,36,54,78,104,136,170,210,252,300,350,406,464,528,594,666, %T A139592 740,820,902,990,1080,1176,1274,1378,1484,1596,1710,1830,1952,2080, %U A139592 2210,2346,2484,2628,2774,2926,3080,3240,3402,3570,3740 %N A139592 A033585(n) followed by A139271(n+1). %C A139592 Sequence found by reading the line from 0, in the direction 0, 2,... and the same line from 0, in the direction 0, 10,..., in the square spiral whose vertices are the triangular numbers A000217. %C A139592 a(n) = 2*A006578(n) - A002378(n)/2 = 2*A035608(n). [From _Reinhard Zumkeller_, Feb 07 2010] %H A139592 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>. %H A139592 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1). %F A139592 Array read by rows: row n gives 8*n^2 + 2n, 8*(n+1)^2 - 6(n+1). %F A139592 a(n) = 2*floor((n + 1/4)^2). [From _Reinhard Zumkeller_, Feb 07 2010] %F A139592 G.f.: 2*x*(1+3*x)/((1-x)^3*(1+x)). [_Colin Barker_, Apr 26 2012] %e A139592 Array begins: %e A139592 0, 2 %e A139592 10, 20 %e A139592 36, 54 %e A139592 78, 104 %Y A139592 Cf. A000217, A033585, A046092, A139271, A077221, A139591, A139593, A139595, A139596, A139597, A139598. %K A139592 easy,nonn %O A139592 0,2 %A A139592 _Omar E. Pol_, May 03 2008