a(n) = 7^n - 6^n - 5^n - 4^n + 3*3^n.

Terms

a(0) =1a(1) =1a(2) =-1a(3) =19a(4) =467a(5) =5611a(6) =53459a(7) =455659a(8) =3648707a(9) =28119691a(10) =211372019a(11) =1562038699a(12) =11405181347a(13) =82545287371a(14) =593501306579