Beginning with 1, a(n) = least number m > a(n-1) such that phi(a(n-1)) divides phi(m).

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =8a(6) =10a(7) =12a(8) =13a(9) =21a(10) =26a(11) =28a(12) =35a(13) =39a(14) =45a(15) =52a(16) =56a(17) =65a(18) =97a(19) =119a(20) =153a(21) =193a(22) =221a(23) =291a(24) =357a(25) =386a(26) =388a(27) =416a(28) =442a(29) =448