A372087 G.f. A(x) satisfies A(x) = 1/( 1 - 9*x*(1 + x)*A(x) )^(1/3).
1, 3, 30, 369, 5130, 76626, 1200816, 19475829, 324140886, 5504511654, 94998663000, 1661370690546, 29377608173460, 524366947411668, 9435112261205328, 170958245619049173, 3116653690408787070, 57125853834377116014, 1052116816793294021688
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n, 9^k*binomial(4*k/3-2/3, k)*binomial(k, n-k)/(k+1));
Formula
a(n) = Sum_{k=0..n} 9^k * binomial(4*k/3-2/3,k) * binomial(k,n-k)/(k+1).