Euclid discovered the first four perfect numbers which are generated by the
formula 2n −1(2n −1), called Euclid number.
In his book ’Elements’ he presented
the proof of the formula which gives an even perfect number whenever 2n − 1 isprime. In order for 2n − 1 to be a prime n must itself be a prime. Moreover, the
perfect numbers are all even and end with 6 or 8