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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 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.)