A072355 Numbers k such that sigma(k) = (Pi^2)*(k/6) rounded off (where 0.5 is rounded to 0).

2, 4, 22, 63, 4202, 4246, 444886, 1161238, 9362914, 26996486, 545614671, 1640386293, 2242930954, 2243031802, 2243065418, 2243115842, 18000691527

Offset

1,1

Comments

In 1838 Dirichlet showed that the average value of sigma(n) is (Pi^2)*(n/6) for large n (see Tattersall).

References

Tattersall, J. "Elementary Number Theory in Nine Chapters", Cambridge University Press, 1999.

Links

Table of n, a(n) for n=1..17.

Example

sigma(444886) = 731808 = (Pi^2 * 444886)/6 rounded off; so 444886 is a term of the sequence.

Mathematica

Select[Range[10^6], Round[(Pi^2 * #)/6] == DivisorSigma[1, # ] &]

Crossrefs

Cf. A013661 (Pi^2/6), A074920.

Sequence in context: A067654 A271944 A152120 * A134246 A254867 A305492

Adjacent sequences: A072352 A072353 A072354 * A072356 A072357 A072358

Keyword

nonn,more

Author

Joseph L. Pe, Jul 18 2002

Extensions

More terms from Robert G. Wilson v, Jul 27 2002

a(10)-a(17) from Giovanni Resta, Apr 03 2017

Status

approved