%I #19 Dec 11 2019 07:40:27
%S 1248,1596,28272,30240,32760,463296,2178540,12865770,23569920,
%T 30998250,45532800,142990848,1379454720,1912369152,2623977450,
%U 43861478400,66433720320,153003540480,403031236608,489622536192,704575228896
%N Numbers m such that m = sigma(abs(k)) - 3k, where k = sigma(m) - 3m.
%C 1.5*10^12 < a(22) <= 7834005405696. If 2^k-1 > 3 is a prime (A000023), then 2^(k-1)*3*19*(2^k-1) is a term. - _Giovanni Resta_, Dec 11 2019
%e Let n = 1248. The sum of the divisors of n is 3528, so k = 3528 - 3*1248 = -216. The sum of the divisors of 216 is 600 and 600 - 3*(-216) = 1248, so 1248 is in the sequence.
%t Select[Range[5*10^5], DivisorSigma[1, Abs[(k = DivisorSigma[1, #] - 3#)]] -3k == # &] (* _Amiram Eldar_, Dec 11 2019 *)
%Y Cf. A000203, A069085, A001065.
%K nonn,more
%O 1,1
%A _Jason Earls_, Apr 08 2002
%E More terms from _David Wasserman_, Apr 15 2003
%E a(12)-a(15) from _Amiram Eldar_, Dec 11 2019
%E a(16)-a(21) from _Giovanni Resta_, Dec 11 2019