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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 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 May 16 08:07 EDT 2021. Contains 343940 sequences. (Running on oeis4.)