A289127 Numbers k such that uphi(k)/uphi(uphi(k)) > uphi(m)/uphi(uphi(m)) for all m < k, where uphi is the unitary totient function (A047994).

1, 3, 7, 31, 211, 2311, 32048, 512768, 9737984, 300690391, 6915878971, 8626257644

Offset

1,2

Links

Table of n, a(n) for n=1..12.

Paul Erdős and M. V. Subbarao, On the iterates of some arithmetic functions, The theory of arithmetic functions (Proc. Conf., Western Michigan Univ., Kalamazoo, Mich. 1971), Lecture Notes in Math., 251, pp. 119-125, Springer, Berlin, 1972. [alternate link]

Mathematica

uphi[n_] := If[n==1, 1, (Times @@ (Table[ #[[1]]^ #[[2]] - 1, {1} ] & /@ FactorInteger[n]))[[1]]]; a = {}; k=1; rmax = 0; While[Length[a]<8, s = uphi[ k]; s2 = uphi[ s]; r = s/s2;  If[r > rmax, AppendTo[a, k]; rmax = r]; k++]; a

Crossrefs

The unitary version of A289125.

Cf. A047994.

Sequence in context: A002585 A365021 A103785 * A289125 A083772 A093441

Adjacent sequences: A289124 A289125 A289126 * A289128 A289129 A289130

Keyword

nonn,more

Author

Amiram Eldar, Jun 25 2017

Extensions

a(10)-a(12) from Amiram Eldar, Mar 26 2023

Status

approved