A199009 - OEIS

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A199009

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

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Arkadiusz Wesolowski, Table of n, a(n) for n = 1..10000

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

Supersequence of A078972 and of A182301.

Sequence in context: A077094 A210441 A343597 * A070807 A246282 A374954

Adjacent sequences: A199006 A199007 A199008 * A199010 A199011 A199012

KEYWORD

base,nonn

AUTHOR

Arkadiusz Wesolowski, Nov 01 2011

STATUS

approved