a(n) = (9*n)!/((3*n)!*(2*n)!) * (n/2)!/(9*n/2)!.A347858a(n) = (9*n)!/((3*n)!*(2*n)!) * (n/2)!/(9*n/2)!.Terms a(0) =1a(1) =512a(2) =1021020a(3) =2399141888External referencesoeis: A347858