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 A139612 #21 Apr 03 2024 17:14:16
%S A139612 12,78,144,210,276,342,408,474,540,606,672,738,804,870,936,1002,1068,
%T A139612 1134,1200,1266,1332,1398,1464,1530,1596,1662,1728,1794,1860,1926,
%U A139612 1992,2058,2124,2190,2256,2322,2388,2454,2520,2586,2652,2718
%N A139612 a(n) = 66*n + 12.
%C A139612 Numbers of the 12th column of positive numbers in the square array of nonnegative and polygonal numbers A139600. Also, numbers of the 12th column in the square array A057145.
%H A139612 Vincenzo Librandi, <a href="/A139612/b139612.txt">Table of n, a(n) for n = 0..5000</a>
%H A139612 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A139612 From _Elmo R. Oliveira_, Apr 03 2024: (Start)
%F A139612 G.f.: 6*(2+9*x)/(x-1)^2.
%F A139612 E.g.f.: 6*exp(x)*(2 + 11*x).
%F A139612 a(n) = 6*A017413(n).
%F A139612 a(n) = 2*a(n-1) - a(n-2) for n >= 2. (End)
%t A139612 66*Range[0,50]+12 (* or *) LinearRecurrence[{2,-1},{12,78},50] (* _Harvey P. Dale_, Jun 14 2017 *)
%o A139612 (Magma) [6*(11*n + 2): n in [0..60]]; // _Vincenzo Librandi_, Jul 23 2011
%o A139612 (PARI) a(n)=66*n+12 \\ _Charles R Greathouse IV_, Oct 05 2011
%Y A139612 Cf. A017413, A057145, A139600.
%K A139612 easy,nonn
%O A139612 0,1
%A A139612 _Omar E. Pol_, Apr 27 2008