# Perfect Numbers in Mathematics

### What are Perfect Numbers ?

Perfect numbers are the natural numbers, whose sum of positive divisors (excluding the number itself) is equal to the number itself.Also, it means that sum of all the factors of the number (including itself) is twice the number.

The first perfect number is 6, because 1, 2, and 3 are its proper positive divisors, and 1 + 2 + 3 = 6. Equivalently, the number 6 is equal to half the sum of all its positive divisors: ( 1 + 2 + 3 + 6 ) / 2 = 6.
List of first few perfect numbers are

6 = 1 + 2 + 3
28 = 1 + 2 + 4 + 7 + 14
496 = 1 + 2 + 4 + 8 + 31 + 62 + 124 + 248

Euclid discovered that the first four perfect numbers are generated by the formula 2p−1(2p−1), with p a prime number:
for p = 2: 21(22−1) = 6
for p = 3: 22(23−1) = 28
for p = 5: 24(25−1) = 496
for p = 7: 26(27−1) = 8128.

Noticing that in each of these cases 2p−1 is a prime number, Euclid proved that 2p−1(2p−1) is an even perfect number whenever 2p−1 is prime . Perfect Number Chart

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What is a prime number ?
What are Even and odd numbers ?

Perfect Numbers Definition

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