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%I #14 Mar 15 2015 18:11:55
%S 1,81,400,32400,195938,224450,1705636,3648100,13645088,15870978,
%T 18180450,29184800,138156516,295496100,1055340196,1105252128,
%U 1476326929,2263475776,2323432804,2363968800,2592846400,2661528100,2686005218,2917410498,3564550178
%N Numbers n such that both sigma(n) and sigma(sigma(n)) are odd numbers.
%C Only members of A028982 are candidates. - _Robert G. Wilson v_, Aug 27 2004
%C Question: iterating sigma()=A000203, how many iterates can be odd numbers?
%H Donovan Johnson, <a href="/A097025/b097025.txt">Table of n, a(n) for n = 1..500</a>
%e n = 1910^2, sigma(n) = 2821^2, sigma(sigma(n)) = 10357983.
%t t = Sort[ Flatten[ Table[{n^2, 2n^2}, {n, 36650}]]]; a = {}; Do[ If[ OddQ[ DivisorSigma[1, DivisorSigma[1, t[[n]] ]]], AppendTo[a, t[[n]] ]], {n, 2*10^6}]; a (* _Robert G. Wilson v_, Aug 27 2004 *)
%Y Cf. A008847, A000203, A097024, A028982.
%K nonn
%O 1,2
%A _Labos Elemer_, Aug 24 2004
%E Edited and extended by _Robert G. Wilson v_, Aug 27 2004
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