a(n) = 6^n-5^n-4^n-3^n-2^n-1.

Terms

a(0) =-4a(1) =-9a(2) =-19a(3) =-9a(4) =317a(5) =3351a(6) =26141a(7) =183111a(8) =1216637a(9) =7842231a(10) =49591901a(11) =309595431a(12) =1915328957a(13) =11771279511a(14) =71987413661a(15) =438579282951