The Fibonacci sequence's adjacent elements are coprime?
That sounds fun to prove.
Let's see... Aha! Take any segment (a b c) in the sequence. We can see that a=c-b. Thus if b and c are both divisible by x, then so is a. We can see that the preceding segment (z a b) will have a and b divisible by x, so z is also divisible by x. We can keep repeating this until we reach the start of the sequence. We can form a statement: if an adjacent pair is both divisible by x, then all preceding elements are also divisible by x. Since the sequence contains 1, then such x other than 1 cannot be found, since 1 would have to be divisible by it.
Or, if b is divisible by x and a isn't (iff this applies for all b's divisors, then b and a are coprime), then c=a+b also isn't divisible by x. So if a and b are coprime, then b and c must also be coprime.
2 and 3 are coprime, so by induction 3 and 5 are, so 5 and 8 are, etc. To infinity. (hmm... I wonder if the statements "0 and 1 are coprime" and "1 and 1 are coprime" are valid.)
That was pretty simple, but fun.