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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
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
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
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.)