a(n) = Sum_{k=0..n} Stirling2(3*n,k).A392772a(n) = Sum_{k=0..n} Stirling2(3*n,k).Terms a(0) =1a(1) =1a(2) =32a(3) =3281a(4) =700075a(5) =255514355a(6) =142508723651External referencesoeis: A392772