A090556 Beginning with 1, a(n) = least number m > a(n-1) such that phi(a(n-1)) divides phi(m).

1, 2, 3, 4, 5, 8, 10, 12, 13, 21, 26, 28, 35, 39, 45, 52, 56, 65, 97, 119, 153, 193, 221, 291, 357, 386, 388, 416, 442, 448, 476, 485, 579, 595, 663, 765, 769, 965, 1105, 1455, 1538, 1544, 1552, 1649, 1799, 2307, 2313, 2895, 3076, 3088, 3104, 3281, 3341, 3845, 4947

Offset: 1

Author

Amarnath Murthy, Dec 10 2003

Keywords

• nonn

Links

• Ivan Neretin, Table of n, a(n) for n = 1..308

Crossrefs

Cf. A014573, A090557.

Programs

Mathematica

NestList[Function[n, SelectFirst[Range[n + 1, 10^4], Divisible[EulerPhi@ #, EulerPhi@ n] &]], 1, 54] (* Michael De Vlieger, May 01 2016, Version 10 *)

Formula

a(1)=1, then a(n+1) = A069797(a(n)). - Ivan Neretin, May 01 2016

Extensions

Corrected and extended by Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 03 2004