A230213 - OEIS

%I #14 Sep 23 2019 11:38:31

%S 25,50,69,81,87,100,115,117,138,145,162,171,174,200,213,230,234,261,

%T 265,276,285,289,290,324,333,339,342,345,348,351,355,357,369,375,385,

%U 391,400,405,415,425,426,445,460,468,475,477,493,505,522,529,530,552,555

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

%H Amiram Eldar, <a href="/A230213/b230213.txt">Table of n, a(n) for n = 1..10000</a>

%e Odious number 100 equals 5*20, such that 5 and 20 are evil. So, 100 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] && ! (evilQ[f[[i]]] && evilQ[n/f[[i]]]), i++]; i <= Length[f]]]; Select[Range[1000], odiousQ[#] && fQ[#] &] (* _T. D. Noe_, Oct 16 2013 *)

%Y Cf. A000069, A001969.

%K nonn,base

%O 1,1

%A _Vladimir Shevelev_, Oct 11 2013

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