this one is not a prime number, because 4,294,967,297 = 641 × 6,700,417. If
we put n = 6 or 7 into the formula the results are huge Fermat numbers but, as
with 5, neither is prime.
Are there any other Fermat primes? The accepted wisdom is that there are
not, but no one knows for sure.

the condensed idea

Take a straight edge and a pair of

compasses...