A366041 Expansion of (1/x) * Series_Reversion( x*(1-x)*(1-x^4) ).
1, 1, 2, 5, 15, 48, 160, 549, 1930, 6919, 25200, 92976, 346757, 1305140, 4951216, 18912245, 72675114, 280761670, 1089800270, 4248149795, 16623209911, 65273370720, 257115465600, 1015719256200, 4023178881540, 15974388769653, 63570826294760
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n\4, binomial(n+k, n)*binomial(2*n-4*k, n))/(n+1);
Formula
a(n) = (1/(n+1)) * Sum_{k=0..floor(n/4)} binomial(n+k,n) * binomial(2*n-4*k,n).