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 A162729 #14 Sep 08 2022 08:45:46
%S A162729 0,10,300,7750,195000,4881250,122062500,3051718750,76293750000,
%T A162729 1907347656250,47683710937500,1192092871093750,29802322265625000,
%U A162729 745058059082031250,18626451489257812500,465661287292480468750
%N A162729 a(n) = 5^n*(5^n-1)/2.
%H A162729 Vincenzo Librandi, <a href="/A162729/b162729.txt">Table of n, a(n) for n = 0..500</a>
%H A162729 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (30, -125).
%F A162729 a(n) = A000217(A000351(n)-1) = 30*a(n-1)-125*a(n-2). G.f.: 10*x/((25*x-1)*(5*x-1)). - _R. J. Mathar_, Jul 13 2009
%t A162729 n5[n_]:=Module[{c=5^n},(c(c-1))/2];Array[n5,20,0] (* or *) LinearRecurrence[ {30,-125},{0,10},20] (* _Harvey P. Dale_, Oct 25 2011 *)
%o A162729 (Magma) [5^n*(5^n-1)/2: n in [0..20]]; // _Vincenzo Librandi_, Mar 05 2012
%K A162729 nonn,easy
%O A162729 0,2
%A A162729 _Vincenzo Librandi_, Jul 12 2009
%E A162729 Edited by _R. J. Mathar_, Jul 13 2009