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23 is a prime number from 1-100. 23 has two factors, 1 and 23. 23 is said to also be one of the numbers that when you add up its digits, you get a prime number. It is the ninth prime number, and the ninth prime number from 1-100.

## Proofs

• — 23 can be divided by 1.
• — 23 cannot be divided by 2-22.
• — 23 can be divided by 23.
• Therefore, 23 has 2 factors.

## As an Exponent of Mersenne Number

223 - 1, which is the number 8,388,607, can be factored into 47 x 178,481, and therefore not a prime number.

## Relationships with other odd numbers

### The numbers before

• The previous odd number, 21, is not a prime number. It is divisible by 3 and 7.
• The odd number previous to 21 is 19. 19 is a prime number.
• 19 and 23 are four numbers apart; therefore, they are cousin primes.
• The odd number previous to 19 is 17. 17 is a prime number.
• 17 and 23 are six numbers apart; therefore, they are sexy primes.

### The numbers after

• The next odd number, 25, is not a prime number. It is a square number, being 52 = 25.
• 27, the odd number following 25, is not a prime number. It is a cube number, being 33 = 27.
• 29, the odd number following 27, is a prime number.
• 23 and 29 are six numbers apart; therefore, they are sexy primes.
• Due to the fact that 23 is not part of any twin numbers, it is considered an isolated prime.