a(n) = 7^n - 5^n + 3^n - 2^n.

Terms

a(0) =0a(1) =3a(2) =29a(3) =237a(4) =1841a(5) =13893a(6) =102689a(7) =747477a(8) =5380481a(9) =38419653a(10) =272767649a(11) =1928673717a(12) =13597673921a(13) =95669893413a(14) =672124323809