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A072355 Numbers k such that sigma(k) = (Pi^2)*(k/6) rounded off (where 0.5 is rounded to 0). 2
2, 4, 22, 63, 4202, 4246, 444886, 1161238, 9362914, 26996486, 545614671, 1640386293, 2242930954, 2243031802, 2243065418, 2243115842, 18000691527 (list; graph; refs; listen; history; text; internal format)
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

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Last modified June 21 04:10 EDT 2021. Contains 345354 sequences. (Running on oeis4.)