a(n) = phi(n^4).

Terms

a(0) =1a(1) =8a(2) =54a(3) =128a(4) =500a(5) =432a(6) =2058a(7) =2048a(8) =4374a(9) =4000a(10) =13310a(11) =6912a(12) =26364a(13) =16464a(14) =27000a(15) =32768a(16) =78608a(17) =34992a(18) =123462a(19) =64000a(20) =111132a(21) =106480a(22) =267674a(23) =110592a(24) =312500a(25) =210912a(26) =354294a(27) =263424a(28) =682892a(29) =216000