A371693 G.f. satisfies A(x) = ( 1 + x * A(x) * (1 + A(x)) )^2.
1, 4, 28, 248, 2480, 26688, 301648, 3531424, 42449088, 520858496, 6497190528, 82146802944, 1050370074624, 13559126110720, 176469550681344, 2313050095245824, 30506619439926272, 404558181197010944, 5391161355764205568, 72156618656648237056, 969557980700415827968
Offset: 0
Keywords
Programs
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PARI
a(n, r=2, t=2, u=2) = r*sum(k=0, n, binomial(n, k)*binomial(t*n+u*k+r, n)/(t*n+u*k+r));
Formula
G.f.: B(x)^2 where B(x) is the g.f. of A219534.
a(n) = Sum_{k=0..n} binomial(n,k) * binomial(2*n+2*k+2,n)/(n+k+1).