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 A256648 #39 Aug 04 2025 11:24:49
%S A256648 0,1,29,110,270,535,931,1484,2220,3165,4345,5786,7514,9555,11935,
%T A256648 14680,17816,21369,25365,29830,34790,40271,46299,52900,60100,67925,
%U A256648 76401,85554,95410,105995,117335,129456,142384,156145,170765,186270,202686,220039,238355
%N A256648 28-gonal pyramidal numbers: a(n) = n*(n+1)*(26*n-23)/6.
%C A256648 See comments in A256645.
%C A256648 This sequence is related to A051867 by a(n) = n*A051867(n) - Sum_{i=0..n-1} A051867(i). - _Bruno Berselli_, Apr 09 2015
%D A256648 E. Deza and M. M. Deza, Figurate numbers, World Scientific Publishing (2012), page 93 (26th row of the table).
%H A256648 Luciano Ancora, <a href="/A256648/b256648.txt">Table of n, a(n) for n = 0..1000</a>
%H A256648 Luciano Ancora, <a href="/A256645/a256645_1.pdf">Polygonal and Pyramidal numbers</a>, Section 3.
%H A256648 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-6,4,-1).
%F A256648 G.f.: x*(1 + 25*x)/(1 - x)^4.
%F A256648 a(n) = A000292(n) + 25*A000292(n-1).
%F A256648 From _Elmo R. Oliveira_, Aug 04 2025: (Start)
%F A256648 E.g.f.: exp(x)*x*(6 + 81*x + 26*x^2)/6.
%F A256648 a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4). (End)
%t A256648 Table[n (n + 1)(26 n - 23)/6, {n, 0, 40}]
%t A256648 LinearRecurrence[{4, -6, 4, -1}, {0, 1, 29, 110}, 40] (* _Vincenzo Librandi_, Apr 08 2015 *)
%o A256648 (Magma) [n*(n+1)*(26*n-23)/6: n in [0..50]]; // _Vincenzo Librandi_, Apr 08 2015
%Y A256648 Partial sums of A161935.
%Y A256648 Cf. similar sequences listed in A237616.
%Y A256648 Cf. A000292, A051867, A256645.
%K A256648 nonn,easy
%O A256648 0,3
%A A256648 _Luciano Ancora_, Apr 07 2015