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%I #19 Dec 09 2024 23:23:41
%S 20,26,41,44,65,83,132,133,140,182,188,195,249,287,299,420,546,564,
%T 620,644,764,806,861,897,1001,1115,1169,1271,28644,32172,35052,39116,
%U 40796,41478,42315,47492,50162,51513,52143,53745,54033,54483,56427,56642
%N Numbers k such that sigma(sigma(sigma(k))) == 6*sigma(k).
%H Harry J. Smith, <a href="/A067065/b067065.txt">Table of n, a(n) for n = 1..146</a>
%t Select[Range[60000],Nest[DivisorSigma[1,#]&,#,3]==6*DivisorSigma[1,#]&] (* _Harvey P. Dale_, Oct 04 2016 *)
%o (PARI) isok(k) = { sigma(sigma(sigma(k))) == 6*sigma(k) } \\ _Harry J. Smith_, May 03 2010
%K nonn
%O 1,1
%A _Benoit Cloitre_, Feb 17 2002
%E Definition corrected by _Harry J. Smith_, May 03 2010
%E Terms added by _Harry J. Smith_, May 03 2010