a(n) = phi(n^9), where phi = A000010.

Terms

a(0) =1a(1) =256a(2) =13122a(3) =131072a(4) =1562500a(5) =3359232a(6) =34588806a(7) =67108864a(8) =258280326a(9) =400000000a(10) =2143588810a(11) =1719926784a(12) =9788768652a(13) =8854734336a(14) =20503125000a(15) =34359738368a(16) =111612119056a(17) =66119763456a(18) =305704134738a(19) =204800000000a(20) =453874312332a(21) =548758735360a(23) =880602513408