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A293712 Numbers n such that psi(phi(n))/n > psi(phi(m))/m for all m < n, where phi is Euler's totient function (A000010) and psi is the Dedekind psi function (A001615). 0
1, 5, 7, 13, 19, 31, 61, 151, 181, 211, 421, 631, 1051, 1471, 2311, 4621, 9241, 11551, 18481, 25411, 32341, 34651, 43891, 60653, 120121, 150151, 180181, 270271, 300301, 330331, 390391, 420421, 450451, 540541, 600601, 660661, 840841, 870871, 1023053, 2045003 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Sândor proved that lim sup psi(phi(n))/n = oo, hence this sequence is infinite.

REFERENCES

Jôzsef Sândor, On Dedekind’s arithmetical function, Seminarul de Teoria Structurilor, Univ. Timisoara, No. 51, 1988, pp. 1-15.

LINKS

Table of n, a(n) for n=1..40.

Jôzsef Sândor, On the composition of some arithmetic functions, II, Journal of Inequalities in Pure and Applied Mathematics, Vol. 6, Issue 3, Article 73 (2005).

MATHEMATICA

psi[n_] := If[n < 1, 0, n*Sum[MoebiusMu[d]^2/d, {d, Divisors@n}]]; a={}; rm=0; Do[r=psi[EulerPhi[n]]/n; If[r>rm, rm=r; AppendTo[a, n]], {n, 1, 100000}]; a

CROSSREFS

Cf. A000010, A001615.

Sequence in context: A006512 A074304 A264865 * A297674 A072677 A117249

Adjacent sequences:  A293709 A293710 A293711 * A293713 A293714 A293715

KEYWORD

nonn

AUTHOR

Amiram Eldar, Oct 15 2017

STATUS

approved

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Last modified April 18 04:49 EDT 2021. Contains 343072 sequences. (Running on oeis4.)