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A074920 Integers k such that phi(k) = 6k/Pi^2 rounded to nearest integer. 2
1, 2, 3, 4, 33, 39, 99, 3237, 9711, 2069301, 6207903, 45502509, 24091595067 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The average value of phi(n) can be approximated for large n by 6n/Pi^2 (Tattersall, p. 162).

REFERENCES

James J. Tattersall, "Elementary Number Theory in Nine Chapters", Cambridge University Press, 2001.

LINKS

Table of n, a(n) for n=1..13.

EXAMPLE

phi(99) = 60 and 6*99/Pi^2 = 60.1848...., which rounds off to 60. Hence 99 is a term of the sequence.

MATHEMATICA

s = Pi^2; l = {}; Do[ If[Abs[EulerPhi[n] - 6 n/ s] <= 0.5, l = Append[l, n]], {n, 1, 10^5}]; l

CROSSREFS

Cf. A000010, A072355.

Cf. A059956 (6/Pi^2).

Sequence in context: A067242 A028354 A028355 * A180631 A102842 A299169

Adjacent sequences:  A074917 A074918 A074919 * A074921 A074922 A074923

KEYWORD

nonn,more

AUTHOR

Joseph L. Pe, Oct 01 2002

EXTENSIONS

a(10)-a(13) from Amiram Eldar, May 10 2019

Name edited by Michel Marcus, May 10 2019

STATUS

approved

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Last modified June 6 17:20 EDT 2020. Contains 334829 sequences. (Running on oeis4.)