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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 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 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.)