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 A237046 Numbers n such that sigma(n) < 2n-1. 3
 3, 5, 7, 9, 10, 11, 13, 14, 15, 17, 19, 21, 22, 23, 25, 26, 27, 29, 31, 33, 34, 35, 37, 38, 39, 41, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 55, 57, 58, 59, 61, 62, 63, 65, 67, 68, 69, 71, 73, 74, 75, 76, 77, 79, 81, 82, 83, 85, 86, 87, 89, 91, 92, 93, 94, 95, 97, 98, 99, 101 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that A235796(n) > 0. Complement of A103288. If the only least-deficient numbers are the powers of 2 (which is an open problem) then the union of A000079 and A023196 and this sequence gives A000027 (see also A103288). LINKS EXAMPLE 10 is in the sequence because the sum of divisors of 10 is less than (2*10 - 1). The sum of divisors of 10 is 1 + 2 + 5 + 10 = 18 and 2*10 - 1 = 19. MATHEMATICA Select[Range[120], DivisorSigma[1, #]<2#-1&] (* Harvey P. Dale, Sep 12 2018 *) PROG (PARI) s=[]; for(n=1, 200, if(sigma(n)<2*n-1, s=concat(s, n))); s \\ Colin Barker, Feb 20 2014 CROSSREFS Cf. A000203, A005100, A023196, A033879, A103288, A196020, A235796, A236104. Sequence in context: A325798 A238524 A237287 * A076212 A085621 A324101 Adjacent sequences:  A237043 A237044 A237045 * A237047 A237048 A237049 KEYWORD nonn,easy AUTHOR Omar E. Pol, Feb 19 2014 STATUS approved

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Last modified May 8 17:26 EDT 2021. Contains 343666 sequences. (Running on oeis4.)