| − | It is relatively straightforward to show that any number '''''P''''' of the form '''''P = 2<sup>n-1</sup> (2<sup>n</sup>-1)''''', for which ('''''2<sup>n</sup>-1''''') is prime, is a perfect number <ref> Proposition IX.36 of Euclid's Elements </ref>. Prime numbers of the form ('''''2<sup>n</sup>-1'''''), for which n is also prime, are called [http://primes.utm.edu/mersenne/ Mersenne Primes], after Marin Mersenne (1588-1648). | + | It is relatively straightforward to show that any number '''''P''''' of the form '''''P = 2<sup>n-1</sup> (2<sup>n</sup>-1)''''', for which ('''''2<sup>n</sup>-1''''') is prime, is a perfect number.<ref>Proposition IX.36 of Euclid's Elements</ref> Prime numbers of the form ('''''2<sup>n</sup>-1'''''), for which n is also prime, are called [http://primes.utm.edu/mersenne/ Mersenne Primes], after Marin Mersenne (1588-1648). |
| | Note that ('''''2<sup>n</sup>-1''''') is not a prime for all prime n, for example ('''''2<sup>11</sup>-1''''') = 2047, which is divisible by 13. The first 12 Mersenne primes are ('''''2<sup>n</sup>-1''''') with: n = 2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107 and 127. | | Note that ('''''2<sup>n</sup>-1''''') is not a prime for all prime n, for example ('''''2<sup>11</sup>-1''''') = 2047, which is divisible by 13. The first 12 Mersenne primes are ('''''2<sup>n</sup>-1''''') with: n = 2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107 and 127. |