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A289126
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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).
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1
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1, 2, 5, 18, 164, 1538, 20018, 408404, 7759748, 148728578, 6976017044, 7317446132
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OFFSET
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1,2
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COMMENTS
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LINKS
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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]
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MATHEMATICA
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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
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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