A373543 Expansion of 1/(1 - x/(1 - 9*x^2)^(2/3)).
1, 1, 1, 7, 13, 64, 151, 634, 1693, 6514, 18688, 68239, 204631, 722920, 2230498, 7711216, 24246229, 82612189, 263112874, 887565955, 2852058448, 9553983613, 30892668295, 102975387211, 334454025715, 1110899344549, 3619669508056, 11992016509234, 39164977065622
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n\2, 9^k*binomial(2*n/3-k/3-1, k));
Formula
a(n) = Sum_{k=0..floor(n/2)} 9^k * binomial(2*n/3-k/3-1,k).
a(n) == 1 (mod 3).