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Evil numbers (A001969) which can be written as a product of two evil numbers > 1.
2

%I #16 Sep 23 2019 11:39:03

%S 9,15,18,27,30,36,45,51,54,60,72,75,85,90,99,102,108,120,129,135,144,

%T 150,153,159,165,170,180,189,195,198,204,207,215,216,225,231,240,243,

%U 249,255,258,267,270,288,297,300,303,306,315,318,325,330,340,360,378

%N Evil numbers (A001969) which can be written as a product of two evil numbers > 1.

%H Amiram Eldar, <a href="/A230306/b230306.txt">Table of n, a(n) for n = 1..10000</a>

%e Evil number 75 = 3*5*5. Since 3 and 5 are evil numbers, than 75 is in the sequence.

%t evilQ[n_] := EvenQ[DigitCount[n, 2][[1]]]; fQ[n_] := Module[{f, i}, If[PrimeQ[n], False, f = Select[Divisors[n], # > 1 && # <= Sqrt[n] &]; i = 1; While[i <= Length[f] && ! (evilQ[f[[i]]] && evilQ[n/f[[i]]]), i++]; i <= Length[f]]]; Select[Range[1000], evilQ[#] && fQ[#] &] (* _T. D. Noe_, Oct 16 2013 *)

%Y Cf. A001969, A227932, A230213, A230226.

%K nonn,base

%O 1,1

%A _Vladimir Shevelev_, Oct 15 2013

%E Extended by _T. D. Noe_, Oct 16 2013

%E a(1)=0 removed by _Amiram Eldar_, Sep 23 2019