Find the rth term of this sequence

1. Jul 21, 2006

Harmony

Given a sequence:
3,33,333,3333,..........
Find the rth term of this sequence.

This sequence does not belong to Geometry Progression or Arithmetic Progression. From what I know, rth term is equals to (r-1)*10 +3.

But how do I solve this problem?

2. Jul 21, 2006

bomba923

Hint:
$$\sum\limits_{k = 0}^n {r^k } = \frac{{1 - r^{n + 1} }}{{1 - r}}$$

The rth term of your sequence is just (10r-1)/3