A373644 a(n) = Sum_{k=0..floor(n/4)} binomial(2*n-7*k,k).
1, 1, 1, 1, 2, 4, 6, 8, 11, 18, 29, 44, 64, 96, 148, 228, 345, 519, 786, 1198, 1824, 2766, 4190, 6358, 9661, 14674, 22268, 33786, 51284, 77866, 118212, 179426, 272333, 413391, 627547, 952613, 1445995, 2194911, 3331793, 5057593, 7677250, 11653681, 17689720
Offset: 0
Links
- Index entries for linear recurrences with constant coefficients, signature (1,0,0,2,0,0,0,-1).
Programs
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PARI
a(n) = sum(k=0, n\4, binomial(2*n-7*k, k));
Formula
G.f.: 1 / (1 - x^4 - x/(1 - x^4)).
a(n) = a(n-1) + 2*a(n-4) - a(n-8) for n > 7.