a(n) = (3*n+1)^7.

Terms

a(0) =1a(1) =16384a(2) =823543a(3) =10000000a(4) =62748517a(5) =268435456a(6) =893871739a(7) =2494357888a(8) =6103515625a(9) =13492928512a(10) =27512614111a(11) =52523350144a(12) =94931877133a(13) =163840000000a(14) =271818611107a(15) =435817657216a(16) =678223072849