A366055 Expansion of (1/x) * Series_Reversion( x*(1-x)^3/(1-x+x^4) ).
1, 2, 7, 30, 144, 741, 3996, 22287, 127494, 743919, 4410255, 26489073, 160843708, 985729010, 6089215057, 37875775533, 237021929322, 1491204370335, 9426547131330, 59843910602283, 381378377720469, 2438954925930558, 15646857920046108
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n\4, binomial(n+1, k)*binomial(3*n-3*k+1, n-4*k))/(n+1);
Formula
a(n) = (1/(n+1)) * Sum_{k=0..floor(n/4)} binomial(n+1,k) * binomial(3*n-3*k+1,n-4*k).