913083596083domain: NAppears in sequencesa(n) = (1/(3^n)^2) * Sum_{k=0..(3^n-1)} binomial(2k,k).at n=2A167912a(n) = A006134(A038754(n) - 1)/3^n.at n=6A320627Numerators of coefficients associated with the second virial coefficient for rigid spheres with imbedded point dipoles.at n=25A336061