a(n) = (2*n + 1)*6^n.

Terms

a(0) =1a(1) =18a(2) =180a(3) =1512a(4) =11664a(5) =85536a(6) =606528a(7) =4199040a(8) =28553472a(9) =191476224a(10) =1269789696a(11) =8344332288a(12) =54419558400a(13) =352638738432