Numbers k such that phi(k) and phi(k+1) are perfect powers (A001597).

Terms

a(0) =1a(1) =15a(2) =16a(3) =63a(4) =101a(5) =125a(6) =255a(7) =256a(8) =272a(9) =504a(10) =512a(11) =513a(12) =629a(13) =679a(14) =1358a(15) =1359a(16) =1728a(17) =1970a(18) =2047a(19) =2222a(20) =2509a(21) =2834a(22) =3458a(23) =3705a(24) =4094a(25) =4095a(26) =4400a(27) =4577a(28) =4616a(29) =4913