Sequence.

1, 2, 5, 14, 42, 132, 429, .......

What rule does this sequence follow?

see: https://en.wikipedia.org/wiki/Catalan_number

Thanks Heureka,

I was wondering about that one.

I was going to look it up in

"Online Encyclopedia of Integer Sequences"  OEIS

but I was on my phone all day so it was too difficult.

I'll do it now :)  

https://oeis.org/search?q=1%2C+2%2C+5%2C+14%2C+42%2C+132%2C+429%2C&language=english&go=Search

It is not at all surprsing that it gives the same answer as Heureka.

OEIS is a great resource, one that is well worth remembering.

 It is mentioned in our Reference material thread, which is in the Sticky topics.  :)