A387623 a(n) = Sum_{k=0..floor(n/4)} 2^k * binomial(2*n-6*k,2*k).
1, 1, 1, 1, 3, 13, 31, 57, 95, 193, 463, 1081, 2295, 4609, 9423, 20185, 44071, 94801, 199807, 418921, 885879, 1889889, 4034639, 8573561, 18155399, 38461105, 81665695, 173627401, 368961431, 783201921, 1661811055, 3527298329, 7490519335, 15908549329, 33779968447
Offset: 0
Links
- Index entries for linear recurrences with constant coefficients, signature (2,-1,0,4,4,0,0,-4).
Programs
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PARI
a(n) = sum(k=0, n\4, 2^k*binomial(2*n-6*k, 2*k));
Formula
G.f.: (1-x-2*x^4)/((1-x-2*x^4)^2 - 8*x^5).
a(n) = 2*a(n-1) - a(n-2) + 4*a(n-4) + 4*a(n-5) - 4*a(n-8).