

A199009


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


2



4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 24, 25, 27, 28, 30, 32, 35, 36, 40, 42, 45, 48, 49, 50, 54, 56, 60, 63, 64, 70, 72, 75, 80, 81, 84, 90, 96, 98, 100, 105, 108, 112, 120, 121, 125, 126, 128, 135, 140, 143, 144, 147, 150, 160, 162, 168, 169, 175, 180
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OFFSET

1,1


LINKS



EXAMPLE

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


MATHEMATICA

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


CROSSREFS



KEYWORD

base,nonn


AUTHOR



STATUS

approved



