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%I #7 Jul 08 2019 12:28:54
%S 1,2,4,6,12,24,36,48,60,72,84,96,108,120,132,144,156,180,192,204,228,
%T 240,252,276,288,300,324,348,360,372,396,444,468,480,492,516,564,576,
%U 588,600,612,636,684,708,720,732,804,828,840,852,876,900,948,960,972,996,1044,1068
%N Numbers k with property that if d divides k, then tau(tau(d)) also divides k.
%C tau() = A000005().
%H Amiram Eldar, <a href="/A141551/b141551.txt">Table of n, a(n) for n = 1..10000</a>
%p with(numtheory); isA141551 := proc(n) local dvs,d; dvs := divisors(n) ; for d in dvs do if not tau(tau(d)) in dvs then RETURN(false): fi; od: RETURN(true); end:
%p t1:=[]; for n from 1 to 60000 do if isA141551(n) then t1:=[op(t1),n]; fi; od:
%t aQ[n_] := AllTrue[Divisors[n], Divisible[n, DivisorSigma[0, DivisorSigma[0, #]]] &]; Select[Range[1000], aQ] (* _Amiram Eldar_, Jul 08 2019 *)
%Y Cf. A000005, A010553, A141586.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Sep 12 2008
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