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 A099515 #3 Mar 30 2012 18:36:43
%S A099515 1,2,5,13,31,78,190,469,1150,2825,6933,17015,41754,102454,251393,
%T A099515 616826,1513453,3713389,9111087,22354678,54848638,134574493,330186518,
%U A099515 810131889,1987705301,4876948743,11965871650,29358946070,72033839657
%N A099515 Row sums of triangle A099514, so that a(n) = Sum_{k=0..n} coefficient of z^k in (1 + z + 2*z^2)^(n-[k/2]), where [k/2] is the integer floor of k/2.
%F A099515 G.f.: (1-2*x^2)/(1-2*x-3*x^2+3*x^3+4*x^4).
%o A099515 (PARI) a(n)=sum(k=0,n,polcoeff((1+x+2*x^2+x*O(x^k))^(n-k\2),k))
%Y A099515 Cf. A099514.
%K A099515 nonn
%O A099515 0,2
%A A099515 _Paul D. Hanna_, Oct 21 2004