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A297364 Numbers n such that f(n) > f(m) for all m < n, where f(n) = usigma(usigma(usigma(n)))/usigma(usigma(n)) and usigma(n) is the sum of unitary divisors of n (A034448). 0
1, 2, 4, 10, 138, 163, 2511, 36943, 408403, 9869857, 11051023 (list; graph; refs; listen; history; text; internal format)
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: A126140 A326967 A223851 * A327059 A012555 A012722

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

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Last modified April 20 01:03 EDT 2021. Contains 343117 sequences. (Running on oeis4.)