a(n) = n^7 - 1.

Terms

a(0) =0a(1) =127a(2) =2186a(3) =16383a(4) =78124a(5) =279935a(6) =823542a(7) =2097151a(8) =4782968a(9) =9999999a(10) =19487170a(11) =35831807a(12) =62748516a(13) =105413503a(14) =170859374a(15) =268435455a(16) =410338672a(17) =612220031a(18) =893871738a(19) =1279999999a(20) =1801088540a(21) =2494357887a(22) =3404825446a(23) =4586471423a(24) =6103515624a(25) =8031810175