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A002659 a(n) = 2*sigma(n) - 1.
(Formerly M3762 N1536)
7
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 (list; graph; refs; listen; history; text; internal format)
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

(PARI) a(n)=if(n<1, 0, 2*sigma(n)-1)

CROSSREFS

Cf. A000203, A002660, A002791, A074400.

A row of the array in A242639.

Sequence in context: A088897 A255233 A074755 * A164122 A166163 A249801

Adjacent sequences:  A002656 A002657 A002658 * A002660 A002661 A002662

KEYWORD

easy,nonn

AUTHOR

N. J. A. Sloane, Simon Plouffe

EXTENSIONS

Better definition from Ralf Stephan, Nov 18 2004

STATUS

approved

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Last modified January 19 17:45 EST 2019. Contains 319309 sequences. (Running on oeis4.)