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 A087405 #9 Aug 29 2025 09:55:38
%S A087405 2,2,22,98,502,2498,12502,62498,312502,1562498,7812502,39062498,
%T A087405 195312502,976562498,4882812502,24414062498,122070312502,610351562498,
%U A087405 3051757812502,15258789062498,76293945312502,381469726562498,1907348632812502,9536743164062498
%N A087405 First differences of A087404: a(n) = A087404(n) - A087404(n-1), a(0) = A087404(0).
%H A087405 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,5).
%F A087405 G.f.: ((1-x)(2-4x))/(1-4x-5x^2).
%F A087405 a(n) = 4*5^(n-1)+2(-1)^n for n > 0.
%F A087405 E.g.f.: 2*(5*cosh(x) + 2*cosh(5*x) - 5*sinh(x) + 2*sinh(5*x) - 2)/5. - _Stefano Spezia_, Aug 29 2025
%t A087405 CoefficientList[Series[((1 - x)(2 - 4x))/(1 - 4x - 5x^2), {x, 0, 25}], x]
%t A087405 LinearRecurrence[{4,5},{2,2,22},30] (* _Harvey P. Dale_, Oct 23 2024 *)
%K A087405 easy,nonn,changed
%O A087405 0,1
%A A087405 Mario Catalani (mario.catalani(AT)unito.it), Sep 01 2003