A297364 Numbers k such that f(k) > f(m) for all m < k, where f(k) = usigma(usigma(usigma(k)))/usigma(usigma(k)) and usigma(k) is the sum of unitary divisors of k (A034448).

1, 2, 4, 10, 138, 163, 2511, 36943, 408403, 9869857, 11051023

Offset

1,2

Comments

1

Links

Table of n, a(n) for n=1..11.

Imre Kátai and M. Wijsmuller, On the iterates of the sum of unitary divisors, Acta Mathematica Hungarica, Vol 79, No. 1-2 (1998), pp. 149-167.

Mathematica

usigma[n_] := Block[{d = Divisors[n]}, Plus @@ Select[d, GCD[ #, n/# ] == 1 &]]; a = {}; k=1; rmax = 0; While[Length[a]<10, s = usigma[ k]; s1=usigma[s]; s2 = usigma[ s1]; r = s2/s1;  If[r > rmax, a = AppendTo[a, k]; rmax = r]; k++]; a

Crossrefs

Cf. A034448.

Sequence in context: A326967 A223851 A371621 * A355203 A327059 A012555

Adjacent sequences: A297361 A297362 A297363 * A297365 A297366 A297367

Keyword

nonn,more

Author

Amiram Eldar, Dec 29 2017

Extensions

a(10) and a(11) from Robert G. Wilson v, Jan 12 2018

Status

approved