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 A139596 #10 Jan 20 2024 17:57:00
%S A139596 0,6,14,28,44,66,90,120,152,190,230,276,324,378,434,496,560,630,702,
%T A139596 780,860,946,1034,1128,1224,1326,1430,1540,1652,1770,1890,2016,2144,
%U A139596 2278,2414,2556,2700,2850,3002,3160,3320,3486,3654,3828
%N A139596 A033587(n) followed by even hexagonal number A014635(n+1).
%C A139596 Sequence found by reading the line from 0, in the direction 0, 6,... and the same line from 0, in the direction 0, 14,..., in the square spiral whose vertices are the triangular numbers A000217.
%H A139596 Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>.
%H A139596 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1).
%F A139596 Array read by rows: row n gives 8*n^2 + 6*n, 8*(n+1)^2 - 2(n+1).
%F A139596 O.g.f.: -2*x*(x+3)/((x-1)^3*(1+x)). - _R. J. Mathar_, May 06 2008
%F A139596 a(n) = 2*A156859(n). - _R. J. Mathar_, Feb 28 2018
%e A139596 Array begins:
%e A139596 0, 6
%e A139596 14, 28
%e A139596 44, 66
%e A139596 90, 120
%t A139596 LinearRecurrence[{2,0,-2,1},{0,6,14,28},50] (* _Harvey P. Dale_, Jan 20 2024 *)
%Y A139596 Cf. A000217, A014635, A033587, A046092, A077221, A139591, A139592, A139593, A139595, A139597, A139598.
%K A139596 easy,nonn
%O A139596 0,2
%A A139596 _Omar E. Pol_, May 03 2008