easy. assume the number to be abc...m and we see that the new number is 10*n +x where x is 0 to 9 so we see that 3n is less 10. So we see that n is 1,2,3

If you consider that $0$ is a natural number (it depends from the country) then it's also a solution : $00=13\cdot0$

we have... 13n = 10n + d --> d is 3n. So n=1 ,2 ,3. glory to god -tony BARKER