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%I #20 Sep 08 2022 08:46:04
%S 46,154,190,2656,6490,44650,318250,1360810,1503370,1788490,3214090,
%T 103712410,3915380170,6077111050,9796360330,10828121356,
%U 33086522327050,35966517350410,11577093570201610,16726040141635450,576460762503970816
%N Numbers n whose deficiency is 20: sigma(n) - 2*n = -20.
%C Suggested by _N. J. A. Sloane_ and _Robert G. Wilson v_.
%C a(17) > 10^12.
%C a(17) > 10^13. - _Giovanni Resta_, Mar 29 2013
%C a(22) > 10^18. - _Hiroaki Yamanouchi_, Aug 21 2018
%C Any term x of this sequence can be combined with any term y of A223611 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
%e n = 1360810. sigma(n)-2*n = -20.
%t Select[Range[1, 10^8], DivisorSigma[1, #] - 2 # == - 20 &] (* _Vincenzo Librandi_, Sep 14 2016 *)
%o (PARI) for(n=1, 10^8, if(sigma(n)-2*n==-20, print1(n ", ")))
%o (Magma) [n: n in [1..9*10^6] | (SumOfDivisors(n)-2*n) eq -20]; // _Vincenzo Librandi_, Sep 14 2016
%Y Cf. A000203, A033879, A223611 (abundance 20).
%K nonn,more
%O 1,1
%A _Donovan Johnson_, Mar 23 2013
%E a(17)-a(21) from _Hiroaki Yamanouchi_, Aug 21 2018
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