A128563 Column 2 of triangle A128562.
1, 4, 12, 29, 61, 120, 222, 392, 669, 1109, 1792, 2838, 4413, 6751, 10184, 15169, 22332, 32538, 46955, 67162, 95288, 134173, 187593, 260562, 359682, 493622, 673736, 914814, 1236057, 1662340, 2225738, 2967500, 3940540, 5212495, 6869598
Offset: 0
Keywords
Programs
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PARI
a(n)=polcoeff(prod(j=n+3,2*n+5,1-q^j)/prod(j=1,n+3,1-q^j),2*n+6,q)
Formula
a(n) is the coefficient of q^(2*n+6) in the q-binomial coefficient [2*n+5, n+2].