A291177 Numbers k such that s(k) = s(k+1) but phi(k) != phi(k+1), where s(k) = phi(k) + phi(phi(k)) + ... + 1 is the sum of iterated phi (A092693).

45, 297, 356, 375, 1335, 1935, 3915, 4743, 5271, 6015, 6375, 6903, 20894, 22311, 25347, 28118, 31664, 32384, 39632, 49155, 50954, 55935, 59984, 64514, 70275, 119324, 125054, 162944, 209715, 334304, 342975, 472718, 767584, 798567, 862802, 908775, 1280096

Offset: 1

Author

Amiram Eldar, Aug 19 2017

Keywords

• nonn

Comments

The restriction phi(k) != phi(k+1) is intended to exclude all the (trivial) terms of A001274.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..200

Crossrefs

Cf. A001274, A092693.

Programs

Mathematica

s[n_]:=Plus @@ FixedPointList[EulerPhi, n] - (n + 1);seqQ[n_]:=(s[n+1]==s[n])&&(EulerPhi[n+1]!=EulerPhi[n]);Select[Range[10^5],seqQ]