a(n) = n^6 - 1.

Terms

a(0) =0a(1) =63a(2) =728a(3) =4095a(4) =15624a(5) =46655a(6) =117648a(7) =262143a(8) =531440a(9) =999999a(10) =1771560a(11) =2985983a(12) =4826808a(13) =7529535a(14) =11390624a(15) =16777215a(16) =24137568a(17) =34012223a(18) =47045880a(19) =63999999a(20) =85766120a(21) =113379903a(22) =148035888a(23) =191102975a(24) =244140624a(25) =308915775a(26) =387420488