Number Theory divisibility proof

[jersiq1]

Homework Statement

Prove that for any n \in Z+, the integer (n(n+1)(n+2) + 21) is divisible by 3

Homework Equations

A previously proved lemma (see below)

The Attempt at a Solution

I sort of just need a nudge here. I have a previously proven lemma which states:

If d|a and d|b, then d|(a+b)

So armed with this I see that obviously 3|21 and all that remains is to prove n(n+1)(n+2) is divisible by 3. I have tried expanding, which didn't seem to help.

 

[VeeEight]

n(n+1)(n+2) is the product of __ consecutive integers.

 

[jersiq1]

Wow! staring me in the face. Thanks.

 

[VeeEight]

Cheers :)