Four consecutive odd numbers can never be primes
True or False?
Bonus : prove it.
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Let there be an odd prime x
Case 1 x ≡ 0 ( m o d 3 )
Either x = 3 or it is composite, as it must be prime ∴ x = 3
Other odd numbers are 5 , 7 , 9
And 9 is not a prime
Case 2 x ≡ 1 ( m o d 3 )
x + 2 ≡ 3 ( m o d 3 ) ⇒ x + 2 ≡ 0 ( m o d 3 ) ⇒ 3 ∣ ( x + 2 )
Therefore either x + 2 = 3 or itis not a prime. If x + 2 = 3 ⇒ x = 1 which is not a prime
Case 3 x ≡ 2 ( m o d 3 )
x + 2 ≡ 4 ( m o d 3 )
x + 4 ≡ 6 ( m o d 3 ) ⇒ x + 4 ≡ 0 ( m o d 3 ) ⇒ 3 ∣ ( x + 4 )
Therefore either x + 4 = 3 or it is not a prime. If x + 4 = 3 ⇒ x = − 1 which is not a prime
∴ Four consecutive odd numbers can never be primes