a(n) = n*(3^(n-1) - 2^(n-1)).

Terms

a(0) =0a(1) =0a(2) =2a(3) =15a(4) =76a(5) =325a(6) =1266a(7) =4655a(8) =16472a(9) =56745a(10) =191710a(11) =638275a(12) =2101188a(13) =6855485a(14) =22205834a(15) =71498775a(16) =229058224a(17) =730680145a(18) =2322163638a(19) =7356008555a(20) =23234743580a(21) =73200452325a(22) =230081633122a(23) =721667902015