Well it obviously isn't true for 1 digit. Try 2:

"ab" = 10a + b

So we want x, y such that

So

which is ridiculous.

So try 3 digits, abc:

So

This, at least, might be possible. We need 29a - b to be divisible by 4 with a and b in the range from 0 - 9. By trial and error I immediately run into (a, b) = (1, 1):

So 711 fits the bill.

See if you can find others.

What can you say about a 4 digit number?

Solve this for d and see if you can find any a, b, c for it and why/why not.

-Dan