Bikerman

Here's a very interesting number: 142,857

Multiply by 2, 3. 4, 5 and 6 and in each case the answer is a rearrangement of the same digits.

Multiply by 7 = 999,999

Multiply by 8 = 1,142,856 - take the 1 from the left and add it to the right (units) - back to the original digits.

Multiply by 9 = 1,285,713 - ditto

Multiply by 11,12,13 ditto

Multiply by 2, 3. 4, 5 and 6 and in each case the answer is a rearrangement of the same digits.

Multiply by 7 = 999,999

Multiply by 8 = 1,142,856 - take the 1 from the left and add it to the right (units) - back to the original digits.

Multiply by 9 = 1,285,713 - ditto

Multiply by 11,12,13 ditto