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 A152777 #28 Dec 24 2024 09:25:06
%S A152777 0,7,49,126,238,385,567,784,1036,1323,1645,2002,2394,2821,3283,3780,
%T A152777 4312,4879,5481,6118,6790,7497,8239,9016,9828,10675,11557,12474,13426,
%U A152777 14413,15435,16492,17584,18711,19873,21070,22302,23569,24871,26208,27580,28987,30429
%N A152777 7 times heptagonal numbers: a(n) = 7*n*(5*n-3)/2.
%C A152777 7 times 7-gonal numbers.
%H A152777 Ivan Panchenko, <a href="/A152777/b152777.txt">Table of n, a(n) for n = 0..1000</a>
%H A152777 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A152777 a(n) = (35*n^2 - 21*n)/2 = 7*A000566(n).
%F A152777 a(n) = a(n-1) + 35*n - 28 (with a(0)=0). - _Vincenzo Librandi_, Dec 15 2010
%F A152777 From _Elmo R. Oliveira_, Dec 24 2024: (Start)
%F A152777 G.f.: 7*x*(1 + 4*x)/(1 - x)^3.
%F A152777 E.g.f.: 7*exp(x)*x*(2 + 5*x)/2.
%F A152777 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n >= 3. (End)
%p A152777 A152777:=n->(35*n^2 - 21*n)/2; seq(A152777(n), n=0..100); # _Wesley Ivan Hurt_, Mar 04 2014
%t A152777 s=0;lst={s};Do[s+=n;AppendTo[lst,s],{n,7,8!,35}];lst (* _Vladimir Joseph Stephan Orlovsky_, Apr 03 2009 *)
%t A152777 7*PolygonalNumber[7,Range[0,40]] (* _Harvey P. Dale_, Jun 03 2024 *)
%o A152777 (Magma) [ 7*n*(5*n-3)/2 : n in [0..50] ]; // _Wesley Ivan Hurt_, Jun 09 2014
%o A152777 (PARI) a(n)=7*n*(5*n-3)/2 \\ _Charles R Greathouse IV_, Jun 17 2017
%Y A152777 Cf. A000566.
%K A152777 easy,nonn
%O A152777 0,2
%A A152777 _Omar E. Pol_, Dec 13 2008