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

Terms

a(0) =0a(1) =10a(2) =136a(3) =1378a(4) =12880a(5) =117370a(6) =1060696a(7) =9559378a(8) =86073760a(9) =774781930a(10) =6973391656a(11) =62761587778a(12) =564857478640