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 A223608 Numbers n whose deficiency is 18: sigma(n) - 2*n = -18. 7
 19, 33, 105, 33705, 33624064, 2199041081344 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Suggested by N. J. A. Sloane and Robert G. Wilson v. a(6) > 10^12. a(7) > 10^13. - Giovanni Resta, Mar 29 2013 a(7) > 10^18. - Hiroaki Yamanouchi, Aug 21 2018 Any term x of this sequence can be combined with any term y of A223610 to satisfy the property (sigma(x)+sigma(y))/(x+y) = 2, which is a necessary (but not sufficient) condition for two numbers to be amicable. - Timothy L. Tiffin, Sep 13 2016 LINKS Table of n, a(n) for n=1..6. EXAMPLE n = 33624064. sigma(n)-2*n = -18. MATHEMATICA Select[Range[1, 10^8], DivisorSigma[1, #] - 2 # == - 18 &] (* Vincenzo Librandi, Sep 14 2016 *) PROG (PARI) for(n=1, 10^8, if(sigma(n)-2*n==-18, print1(n ", "))) (Magma) [n: n in [1..9*10^6] | (SumOfDivisors(n)-2*n) eq -18]; // Vincenzo Librandi, Sep 14 2016 CROSSREFS Cf. A000203, A033879, A223610 (abundance 18). Sequence in context: A152088 A362410 A106527 * A146438 A146571 A235869 Adjacent sequences: A223605 A223606 A223607 * A223609 A223610 A223611 KEYWORD nonn,more AUTHOR Donovan Johnson, Mar 23 2013 EXTENSIONS a(6) from Giovanni Resta, Mar 29 2013 STATUS approved

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Last modified February 21 08:45 EST 2024. Contains 370228 sequences. (Running on oeis4.)