A227932 - OEIS

%I #23 Sep 23 2019 11:39:29

%S 77,147,154,169,175,209,231,245,275,287,294,308,325,329,338,343,350,

%T 399,407,413,418,427,441,455,462,469,483,490,525,533,550,553,567,574,

%U 588,605,609,616,649,650,658,676,679,686,700,703,715,735,759,763,777,798

%N Evil numbers (A001969) which can be written as a product of two odious numbers (A000069).

%H Amiram Eldar, <a href="/A227932/b227932.txt">Table of n, a(n) for n = 1..10000</a>

%e Evil number 275 = 25*11. Since 25 and 11 are odious, then 275 is in the sequence.

%t evilQ[n_] := EvenQ[DigitCount[n, 2][[1]]]; odiousQ[n_] := OddQ[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] && ! (odiousQ[f[[i]]] && odiousQ[n/f[[i]]]), i++]; i <= Length[f]]]; Select[Range[1000], evilQ[#] && fQ[#] &] (* _T. D. Noe_, Oct 16 2013 *)

%Y Cf. A001969, A000069, A230213, A230226.

%K nonn,base

%O 1,1

%A _Vladimir Shevelev_, Oct 15 2013

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