Write any 3 digit number next to itself. For example, 369369.
The resultant 6 digit number is divisible by 7, 11 and 13.
And if you progressively divide the six digit number by 7, 11, and 13, the final result is the original 3 digit number.
369369 ÷ 7 = 52767
52767 ÷ 11 = 4797
4797 ÷ 13 = 369.