a(n) = (16-9*8^n)/7.

Terms

a(0) =1a(1) =-8a(2) =-80a(3) =-656a(4) =-5264a(5) =-42128a(6) =-337040a(7) =-2696336a(8) =-21570704a(9) =-172565648a(10) =-1380525200a(11) =-11044201616a(12) =-88353612944a(13) =-706828903568