A289126 Numbers n such that usigma(usigma(n))/usigma(n) > usigma(usigma(m))/usigma(m) for all m < n, where usigma(n) is the sum of unitary divisors of n (A034448).

1, 2, 5, 18, 164, 1538, 20018, 408404, 7759748, 148728578, 6976017044, 7317446132

Offset

1,2

Comments

The unitary version of A289124.

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

usigma[n_] := If[n == 1, 1, Times @@ (1 + Power @@@ FactorInteger[n])]; a = {}; k=1; rmax = 0; While[Length[a]<8, s = usigma[ k]; s2 = usigma[ s]; r = s2/s;  If[r > rmax, AppendTo[a, k]; rmax = r]; k++]; a

Crossrefs

Cf. A034448, A055033, A289124.

Sequence in context: A281532 A097584 A197855 * A062097 A356366 A323706

Adjacent sequences: A289123 A289124 A289125 * A289127 A289128 A289129

Keyword

nonn,more

Author

Amiram Eldar, Jun 25 2017

Extensions

a(10)-a(12) from Giovanni Resta, Aug 23 2017

Status

approved