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 A263418 #11 Mar 12 2017 08:38:38
%S A263418 1,6,21,51,106,201,361,626,1061,1771,2926,4801,7841,12766,20741,33651,
%T A263418 54546,88361,143081,231626,374901,606731,981846,1588801,2570881,
%U A263418 4159926,6731061,10891251,17622586,28514121,46137001,74651426,120788741,195440491,316229566
%N A263418 a(n) is the total number of pentagrams in a variant of pentagram fractal after n iterations.
%C A263418 Inspired by A255870.
%H A263418 Colin Barker, <a href="/A263418/b263418.txt">Table of n, a(n) for n = 0..1000</a>
%H A263418 Kival Ngaokrajang, <a href="/A263418/a263418.pdf">Illustration of initial terms</a>
%H A263418 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2,-1,1).
%F A263418 a(0) = 1, for n > 0, a(n) = a(n-1) + 5*(fibonacci(n+3)-2) or a(n) = a(n-1) + 5*A001911(n).
%F A263418 From _Colin Barker_, Oct 18 2015: (Start)
%F A263418 a(n) = 3*a(n-1)-2*a(n-2)-a(n-3)+a(n-4) for n>3.
%F A263418 G.f.: -(x^3+5*x^2+3*x+1) / ((x-1)^2*(x^2+x-1)).
%F A263418 (End)
%F A263418 a(n) = -14 + 2^(-1-n)*((25-11*sqrt(5))*(1-sqrt(5))^n + (1+sqrt(5))^n*(25+11*sqrt(5))) - 10*(1+n). - _Colin Barker_, Mar 12 2017
%o A263418 (PARI) {a=1; print1(a, ", "); for(n=1,100, b=fibonacci(n+3)-2; a=a+5*b; print1 (a, ", "))}
%o A263418 (PARI) Vec(-(x^3+5*x^2+3*x+1)/((x-1)^2*(x^2+x-1)) + O(x^50)) \\ _Colin Barker_, Oct 18 2015
%Y A263418 Cf. A001911, A255870, A256429, A256569, A256571, A256582, A256583, A263419.
%K A263418 nonn,easy
%O A263418 0,2
%A A263418 _Kival Ngaokrajang_, Oct 17 2015