A113283 Even bisection of A113281: a(n) = A113281(2*n).
1, 3, 11, 51, 255, 1325, 7039, 37951, 206799, 1135969, 6279509, 34889553, 194664283, 1089943229, 6120967411, 34463104999, 194474062663, 1099571123853, 6227893795649, 35329149864161, 200691916063033, 1141489886332555
Offset: 0
Keywords
Programs
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PARI
{a(n)=local(x=X+X*O(X^n));polcoeff( ((1+x)/(1-x)/(1-6*x+x^2)*(1-x+(1-6*x+x^2)^(1/2))/2)^(1/2),n,X)}
Formula
G.f.: ( (1+x)/(1-x)/(1-6*x+x^2)*(1-x+(1-6*x+x^2)^(1/2))/2 )^(1/2).
a(n) ~ (1 + sqrt(2))^(2*n + 1/2) / (2*sqrt(Pi*n)). - Vaclav Kotesovec, Oct 18 2020