A333610 Least number that reaches 1 after n iterations of the infinitary totient function A091732.

1, 2, 3, 4, 5, 11, 17, 47, 85, 227, 257, 919, 1229, 2459, 4369, 9839, 30865, 101503, 148157, 438499, 828297, 2201671, 3316617, 11055391, 35354993, 140810491, 188991053, 377982107, 848170377, 1704741139, 6933926513

Offset: 0

Author

Amiram Eldar, Mar 28 2020

Keywords

• nonn
• more

Crossrefs

Cf. A003271, A007755, A091732, A333609.

Programs

Mathematica

f[p_, e_] := p^(2^(-1 + Position[Reverse @ IntegerDigits[e, 2], 1])); iphi[1] = 1; iphi[n_] := Times @@ (Flatten@(f @@@ FactorInteger[n]) - 1); numiter[n_] := Length @ NestWhileList[iphi, n, # != 1 &] - 1; n = 0; seq = {}; Do[If[numiter[k] == n, AppendTo[seq, k]; n++], {k, 1, 1000}]; seq

Formula

A333609(a(n)) = n.