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31 is a prime number from 1-100. 31 has 2 factors, 1 and 31. It is said to be a number wherein when digits are added together, they make a composite number. It is the eleventh prime number, and the eleventh prime number from 1-100. 

31-D

It is also the second pi-prime (First is 3).

Proofs[]

  • Yes — 31 can be divided by 1.
  • No — 31 cannot be divided by 2-30.
  • Yes — 31 can be divided by 31.


As an Exponent of Mersenne Number[]

231 - 1, which is the number 2,147,483,647, is a prime number. It is the 8th Mersenne Prime.

​Relationship with other odd numbers[]

The numbers before[]

  • The previous odd number, 29, is a prime number.
    • There are no odd numbers between 29 and 31. As a result, they are twin primes.
  • Before 29, the previous two odd numbers are 25 and 27. 25 is a square number, being 52 = 25. 27 is a cube number, being 33 = 27.
  • The prime number previous to 29 is 23.

The numbers after[]

  • The next odd number, 33, is not a prime number. It is divisible by 3 and 11.
  • The next odd number, 35, is also not a prime number. It is divisible by 5 and 7.
  • 37, the odd number following 35, is a prime number.
    • 31 and 37 are six numbers apart; therefore, they are sexy primes.
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