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 A116409 #7 May 30 2016 12:35:49 %S A116409 1,2,5,13,36,102,294,855,2502,7352,21670,64021,189489,561680,1666955, %T A116409 4952243,14725010,43815836,130462322,388670993,1158491411,3454558976, %U A116409 10305303341,30752447207,91798204811,274101391202,818652308999 %N A116409 Expansion of (1-x-2x^2+sqrt(1-2x-3x^2))/(2(1-x)(1-2x-3x^2)). %C A116409 Row sums of A116407. Binomial transform of A116406. %F A116409 Conjecture: n*a(n) +2*(-3*n+2)*a(n-1) +2*(4*n-5)*a(n-2) +6*(n-2)*a(n-3) +9*(-n+2)*a(n-4)=0. - _R. J. Mathar_, Nov 11 2014 %F A116409 a(n) ~ 3^n/4 * (1 + 3*sqrt(3/(Pi*n))/2). - _Vaclav Kotesovec_, May 30 2016 %Y A116409 Cf. A116410. %K A116409 easy,nonn %O A116409 0,2 %A A116409 _Paul Barry_, Feb 13 2006