Copyright © University of Cambridge. All rights reserved.

## 'Weekly Problem 22 - 2008' printed from http://nrich.maths.org/

The following sequence continues indefinitely:

27 = 3 x 3 x 3

207 = 3 x 3 x 23

2,007 = 3 x 3 x 223

20,007 = 3 x 3 x 2223.......

Which of the following integers is a multiple of 81?

A: 200,007

B: 20,000,007

C: 2,000,000,007

D: 200,000,000,007

E: 20,000,000,000,007

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

*This problem is taken from the UKMT Mathematical Challenges.*

View the previous week's solutionView the current weekly problem