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 A239426 #15 Sep 08 2022 08:46:07
%S A239426 1,3,133,931,3441,9211,20293,39243,69121,113491,176421,262483,376753,
%T A239426 524811,712741,947131,1235073,1584163,2002501,2498691,3081841,3761563,
%U A239426 4547973,5451691,6483841,7656051,8980453,10469683,12136881,13995691,16060261,18345243
%N A239426 21*n^4 - 36*n^3 + 25*n^2 - 8*n + 1.
%C A239426 For n > 0: a(n) = A219069(2*n-1,n).
%H A239426 Reinhard Zumkeller, <a href="/A239426/b239426.txt">Table of n, a(n) for n = 0..10000</a>
%H A239426 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (5,-10,10,-5,1).
%F A239426 a(n) = (1-3*n+3*n^2) * (1-5*n+7*n^2) = A003215(n-1) * A239449(n).
%F A239426 G.f.: ( -1+2*x-128*x^2-286*x^3-91*x^4 ) / (x-1)^5 . - _R. J. Mathar_, Mar 31 2014
%t A239426 Table[(21 n^4 - 36 n^3 + 25 n^2 - 8 n + 1), {n, 0, 40}] (* _Vincenzo Librandi_, Mar 21 2014 *)
%t A239426 LinearRecurrence[{5,-10,10,-5,1},{1,3,133,931,3441},40] (* _Harvey P. Dale_, May 04 2016 *)
%o A239426 (Haskell)
%o A239426 a239426 n = (((21 * n - 36) * n + 25) * n - 8) * n + 1
%o A239426 (Magma) [21*n^4-36*n^3+25*n^2-8*n+1: n in [0..31]]; // _Vincenzo Librandi_, Mar 21 2014
%K A239426 nonn,easy
%O A239426 0,2
%A A239426 _Reinhard Zumkeller_, Mar 19 2014