A135870 G.f. A(x) = (1 + x*A(3x))^2.
1, 2, 13, 246, 13554, 2210436, 1076561037, 1570714992558, 6871883750090694, 90179738434097457084, 3550105797469080332658354, 419263945026939228053105930844, 148543119421079567735277052592081220
Offset: 0
Keywords
Programs
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PARI
{a(n)=local(A=1+x+x*O(x^n));for(i=0,n,A=1+x*subst(A,x,3*x)^2);polcoeff(A^2,n)}
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