A366070 Expansion of (1/x) * Series_Reversion( x*(1+x-x^2)/(1+x)^5 ).
1, 4, 23, 155, 1143, 8932, 72682, 609348, 5227035, 45659020, 404756300, 3632075109, 32928392154, 301152242600, 2775117150576, 25741623112539, 240162703635495, 2252187478291088, 21217451539791085, 200709823787548845, 1905712342347978340
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n\2, binomial(n+k, k)*binomial(4*n-k+4, n-2*k))/(n+1);
Formula
a(n) = (1/(n+1)) * Sum_{k=0..floor(n/2)} binomial(n+k,k) * binomial(4*n-k+4,n-2*k).