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.
1, 2, 5, 13, 31, 78, 190, 469, 1150, 2825, 6933, 17015, 41754, 102454, 251393, 616826, 1513453, 3713389, 9111087, 22354678, 54848638, 134574493, 330186518, 810131889, 1987705301, 4876948743, 11965871650, 29358946070, 72033839657
Offset: 0
Keywords
Crossrefs
Cf. A099514.
Programs
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PARI
a(n)=sum(k=0,n,polcoeff((1+x+2*x^2+x*O(x^k))^(n-k\2),k))
Formula
G.f.: (1-2*x^2)/(1-2*x-3*x^2+3*x^3+4*x^4).