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A063139 Composite numbers which in base 3 contain their largest proper factor as a substring. 0

%I

%S 9,15,21,27,33,39,45,49,51,57,63,69,75,81,87,93,99,105,111,117,123,

%T 129,135,141,147,153,159,165,171,177,183,189,195,201,207,213,219,225,

%U 231,237,243,249,255,261,267,273,279,285,291,297

%N Composite numbers which in base 3 contain their largest proper factor as a substring.

%t Do[ If[ !PrimeQ[ n ] && StringPosition[ ToString[ FromDigits[ IntegerDigits[ n, 3 ] ] ], ToString[ FromDigits[ IntegerDigits[ Divisors[ n ] [ [ -2 ] ], 3 ] ] ] ] != {}, Print[ n ] ], {n, 2, 10^2} ]

%Y Cf. A062238.

%K base,nonn

%O 1,1

%A _Robert G. Wilson v_, Aug 08 2001

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Last modified October 27 01:36 EDT 2021. Contains 348270 sequences. (Running on oeis4.)