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 A152257 #16 May 22 2023 02:51:15
%S A152257 0,1,40,1183,32800,893101,24180520,653473003,17649155200,476575627801,
%T A152257 12867977828200,347439324082423,9380897054183200,253284538196972101,
%U A152257 6838685390919695080,184644531291230453443,4985402576490767372800,134605871649898496094001
%N A152257 a(n) = (3^n - 1)^2*(3^n + 1)/16.
%H A152257 Robert Israel, <a href="/A152257/b152257.txt">Table of n, a(n) for n = 0..698</a>
%H A152257 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (40,-390,1080,-729).
%F A152257 a(n) = (3^n - 1)*(3^n - 1)*(3^n + 1)/16.
%F A152257 G.f.: x*(1-27*x^2)/((1-x)*(1-3*x)*(1-9*x)*(1-27*x)). - _Robert Israel_, Mar 18 2019
%F A152257 a(n) = 40*a(n-1) - 390*a(n-2) + 1080*a(n-3) - 729*a(n-4) for n>3. - _Colin Barker_, Mar 18 2019
%F A152257 From _G. C. Greubel_, May 22 2023: (Start)
%F A152257 a(n) = A002452(n)*A003462(n).
%F A152257 a(n) = A007051(n)*A238976(n+1)/2.
%F A152257 E.g.f.: (1/16)*(exp(x) - exp(3*x) - exp(9*x) + exp(27*x)). (End)
%p A152257 seq((3^n-1)^2*(3^n+1)/16,n=0..30); # _Robert Israel_, Mar 18 2019
%t A152257 Table[(9^n-1)*(3^n-1)/16, {n,0,30}]
%o A152257 (PARI) concat(0, Vec(x*(1 - 27*x^2) / ((1 - x)*(1 - 3*x)*(1 - 9*x)*(1 - 27*x)) + O(x^20))) \\ _Colin Barker_, Mar 18 2019
%o A152257 (Magma) [(9^n-1)*(3^n-1)/16: n in [0..40]]; // _G. C. Greubel_, May 22 2023
%o A152257 (SageMath) [(9^n-1)*(3^n-1)//16 for n in range(41)] # _G. C. Greubel_, May 22 2023
%Y A152257 Cf. A002452, A003462, A007051, A238976.
%K A152257 nonn,easy
%O A152257 0,3
%A A152257 _Roger L. Bagula_, Dec 01 2008
%E A152257 0 inserted by _Robert Israel_, Mar 18 2019