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 A153797 #20 May 16 2025 20:12:14
%S A153797 0,7,56,147,280,455,672,931,1232,1575,1960,2387,2856,3367,3920,4515,
%T A153797 5152,5831,6552,7315,8120,8967,9856,10787,11760,12775,13832,14931,
%U A153797 16072,17255,18480,19747,21056,22407,23800,25235,26712,28231
%N A153797 7 times octagonal numbers: a(n) = 7*n*(3*n-2).
%H A153797 G. C. Greubel, <a href="/A153797/b153797.txt">Table of n, a(n) for n = 0..1000</a>
%H A153797 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A153797 a(n) = 21*n^2 - 14*n = 7*A000567(n).
%F A153797 a(n) = a(n-1) + 42*n - 35 (with a(0)=0). - _Vincenzo Librandi_, Nov 27 2010
%F A153797 From _G. C. Greubel_, Aug 29 2016: (Start)
%F A153797 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3).
%F A153797 G.f.: 7*x*(1 + 5*x)/(1 - x)^3.
%F A153797 E.g.f.: 7*x*(1 + 3*x)*exp(x). (End)
%t A153797 s=0;lst={s};Do[s+=n;AppendTo[lst,s],{n,7,8!,42}];lst (* _Vladimir Joseph Stephan Orlovsky_, Apr 03 2009 *)
%t A153797 Table[7*n*(3*n-2), {n,0,25}] (* or *) LinearRecurrence[{3,-3,1},{0,7,56},25] (* _G. C. Greubel_, Aug 29 2016 *)
%t A153797 7*PolygonalNumber[8,Range[0,40]] (* _Harvey P. Dale_, May 16 2025 *)
%o A153797 (Magma) [ 7*n*(3*n-2): n in [0..40] ];
%o A153797 (PARI) a(n)=7*n*(3*n-2) \\ _Charles R Greathouse IV_, Aug 29 2016
%Y A153797 Cf. A000567 (octagonal numbers), A153796, A153808.
%K A153797 easy,nonn
%O A153797 0,2
%A A153797 _Omar E. Pol_, Jan 20 2009