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 A166725 #21 Feb 26 2022 09:19:32
%S A166725 1,75,3125,109375,3515625,107421875,3173828125,91552734375,
%T A166725 2593994140625,72479248046875,2002716064453125,54836273193359375,
%U A166725 1490116119384765625,40233135223388671875,1080334186553955078125,28870999813079833984375,768341124057769775390625
%N A166725 a(n) = (2*n+1)*25^n.
%H A166725 Vincenzo Librandi, <a href="/A166725/b166725.txt">Table of n, a(n) for n = 0..200</a>
%H A166725 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (50,-625).
%F A166725 G.f.: (1+25*x)/(1-25*x)^2.
%F A166725 Sum_{k>=0} 1/a(k) = (5/2)*log(3/2).
%F A166725 E.g.f.: (50*x + 1)*exp(25*x). - _G. C. Greubel_, May 24 2016
%F A166725 Sum_{n>=0} (-1)^n/a(n) = 5*arctan(1/5). - _Amiram Eldar_, Feb 26 2022
%t A166725 Table[5^(2*n) *(2*n + 1), {n,0,10}] (* _G. C. Greubel_, May 24 2016 *)
%t A166725 LinearRecurrence[{50,-625},{1,75},30] (* _Harvey P. Dale_, Mar 02 2018 *)
%o A166725 (PARI) a(n)=(2*n+1)*25^n
%o A166725 (Magma) [(2*n+1)*25^n: n in [0..20]]; // _Vincenzo Librandi_, Jun 08 2011
%Y A166725 Cf. A058962 ((2n+1)*4^n), A155988 ((2n+1)*9^n), A016578 (log(3/2)).
%K A166725 nonn
%O A166725 0,2
%A A166725 _Jaume Oliver Lafont_, Oct 20 2009