if x = 1
then -x = -1
if we add x2 to both sides:
x2-x = x2-1
and factorise...
x(x-1) = (x+1)(x-1)
now strike out the same terms on each side:
x(x-1) = (x+1)(x-1)
leaving x = x+1
remember x=1, so substitute 1 for x and you get... 1 = 2
...and this is just lovely:
n2 + n + 41
What does it do?
Substitute any positive number less than 40 for n.
Yes, it's a formula that dishes out prime numbers. Leonhard Euler stumbled across this cutie.