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

9, 15, 21, 27, 33, 39, 45, 49, 51, 57, 63, 69, 75, 81, 87, 93, 99, 105, 111, 117, 123, 129, 135, 141, 147, 153, 159, 165, 171, 177, 183, 189, 195, 201, 207, 213, 219, 225, 231, 237, 243, 249, 255, 261, 267, 273, 279, 285, 291, 297

Offset

1,1

Links

Table of n, a(n) for n=1..50.

Mathematica

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

Crossrefs

Cf. A062238.

Sequence in context: A139787 A225461 A172181 * A163170 A097636 A179384

Adjacent sequences: A063136 A063137 A063138 * A063140 A063141 A063142

Keyword

base,nonn

Author

Robert G. Wilson v, Aug 08 2001

Status

approved