A383355 Expansion of 1/sqrt( (1-x) * (1-x-4*x^4) ).
1, 1, 1, 1, 3, 5, 7, 9, 17, 31, 51, 77, 129, 227, 391, 641, 1067, 1829, 3157, 5351, 9033, 15399, 26471, 45349, 77387, 132293, 227153, 390379, 670013, 1149819, 1976595, 3402137, 5856157, 10079327, 17358491, 29918957, 51590271, 88971985, 153484661, 264898703, 457374335
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n\4, binomial(2*k, k)*binomial(n-3*k, k));
Formula
a(n) = Sum_{k=0..floor(n/4)} binomial(2*k,k) * binomial(n-3*k,k).