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A297364
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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).
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0
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1, 2, 4, 10, 138, 163, 2511, 36943, 408403, 9869857, 11051023
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OFFSET
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1,2
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COMMENTS
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1
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LINKS
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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.
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MATHEMATICA
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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
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CROSSREFS
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Cf. A034448.
Sequence in context: A126140 A326967 A223851 * A327059 A012555 A012722
Adjacent sequences: A297361 A297362 A297363 * A297365 A297366 A297367
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KEYWORD
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nonn,more
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AUTHOR
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Amiram Eldar, Dec 29 2017
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EXTENSIONS
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a(10) and a(11) from Robert G. Wilson v, Jan 12 2018
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STATUS
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approved
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