A074920 Integers k such that phi(k) = 6k/Pi^2 rounded to nearest integer.

1, 2, 3, 4, 33, 39, 99, 3237, 9711, 2069301, 6207903, 45502509, 24091595067

Offset: 1

Author

Joseph L. Pe, Oct 01 2002

Keywords

• nonn
• more

Comments

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

Examples

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

References

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

Crossrefs

Cf. A000010, A072355.

Cf. A059956 (6/Pi^2).

Programs

Mathematica

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

Extensions

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

Name edited by Michel Marcus, May 10 2019