Thread: Recursive Formula

How many ten digit integers can be formed using only the numbers 1 & 2 and not having any 1s next to each other?
example: 1222222221 <----- good; 1222211222 <----- no good

What would the recursive formula be that describes this situation?

Thanks in advance for any input!

Originally Posted by MATNTRNG

How many ten digit integers can be formed using only the numbers 1 & 2 and not having any 1s next to each other?
example: 1222222221 <----- good; 1222211222 <----- no good

What would the recursive formula be that describes this situation?

Thanks in advance for any input!

Here's a hint: The Fibonacci sequence.