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

Terms

a(0) =2a(1) =7a(2) =37a(3) =253a(4) =1873a(5) =13957a(6) =102817a(7) =747733a(8) =5380993a(9) =38420677a(10) =272769697a(11) =1928677813a(12) =13597682113a(13) =95669909797a(14) =672124356577