a(n) = 3^(n^2+2n+1)*Product_{j=1..n} (9^j-1).A092301a(n) = 3^(n^2+2n+1)*Product_{j=1..n} (9^j-1).Terms a(0) =3a(1) =648a(2) =12597120External referencesoeis: A092301