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

Terms

a(0) =-3a(1) =-5a(2) =-5a(3) =25a(4) =271a(5) =1825a(6) =10735a(7) =59425a(8) =318271a(9) =1670785a(10) =8656975a(11) =44454625a(12) =226827871a(13) =1151991745a(14) =5830280815a(15) =29429454625a(16) =148249811071a(17) =745630312705