A002659 - OEIS

A002659

a(n) = 2*sigma(n) - 1.
(Formerly M3762 N1536)

1, 5, 7, 13, 11, 23, 15, 29, 25, 35, 23, 55, 27, 47, 47, 61, 35, 77, 39, 83, 63, 71, 47, 119, 61, 83, 79, 111, 59, 143, 63, 125, 95, 107, 95, 181, 75, 119, 111, 179, 83, 191, 87, 167, 155, 143, 95, 247, 113, 185, 143, 195, 107, 239, 143, 239, 159, 179, 119, 335, 123, 191

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OFFSET

1,2

REFERENCES

P. A. MacMahon, The connexion between the sum of the squares of the divisors and the number of partitions of a given number, Messenger Math., 54 (1924), 113-116. Collected Papers, MIT Press, 1978, Vol. I, pp. 1364-1367.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16384

N. J. A. Sloane, Transforms

Index entries for sequences related to sigma(n)

FORMULA

G.f. for Moebius transf.: (x + 2x^2 - x^3 ) / (1 - x )^2.

a(n) = A074400(n) - 1. - Filip Zaludek, Oct 30 2016

MATHEMATICA

2DivisorSigma[1, Range[70]]-1 (* Harvey P. Dale, Apr 14 2014 *)

PROG