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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
1, 2, 5, 18, 164, 1538, 20018, 408404, 7759748, 148728578, 6976017044, 7317446132
OFFSET
1,2
COMMENTS
The unitary version of A289124.
LINKS
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
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Jun 25 2017
EXTENSIONS
a(10)-a(12) from Giovanni Resta, Aug 23 2017
STATUS
approved