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A199009 Composite numbers whose prime factors have an equal number of digits in decimal representation. 2

%I #19 Nov 06 2013 15:35:32

%S 4,6,8,9,10,12,14,15,16,18,20,21,24,25,27,28,30,32,35,36,40,42,45,48,

%T 49,50,54,56,60,63,64,70,72,75,80,81,84,90,96,98,100,105,108,112,120,

%U 121,125,126,128,135,140,143,144,147,150,160,162,168,169,175,180

%N Composite numbers whose prime factors have an equal number of digits in decimal representation.

%H Arkadiusz Wesolowski, <a href="/A199009/b199009.txt">Table of n, a(n) for n = 1..10000</a>

%e 42 = 2*3*7 belongs to this sequence, since its prime factors all have one digit.

%t f[n_] := Length[Union[Length /@ IntegerDigits /@ Transpose[FactorInteger[n]][[1]]]] == 1; Select[Range[2, 180], ! PrimeQ[#] && f[#] &] (* _T. D. Noe_, Nov 01 2011 *)

%Y Supersequence of A078972 and of A182301.

%K base,nonn

%O 1,1

%A _Arkadiusz Wesolowski_, Nov 01 2011

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