a(n) = Stirling_2(n,3)^2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =36a(5) =625a(6) =8100a(7) =90601a(8) =933156a(9) =9150625a(10) =87048900a(11) =812307001a(12) =7486748676a(13) =68447640625a(14) =622473660900