As perfectly explained by
chetan2u Sir,
All prime numbers greater than 3 can be written as 6n+/-1 or 4n+/-1.
But vice versa is not truefor example, for n =4, 6*4+1= 25 , but it is not prime
Similarly, for n = 2, 4n+1 = 2*4+1= 9, which is not prime
In fact, there is no direct formula, which can find whether a number is prime or not.
All prime numbers greater than 3 can be written as 6n+/-1 or 4n+/-1, but all numbers in form of 6n+/-1 or 4n+/-1 are not prime.
Gmatprep550 wrote:
Hi
chetan2u,
Bunuel,
VeritasKarishma,
Gladiator59,
generisFor question 23 statement 7-8
I am only able to find that "All the prime numbers greater than 3 can be written as either 6n+1 or 6n-1." Not able to find anything for 6+1 and 4n+1 or 4n-1.
Could you please review and advise if I am missing something.
stonecold wrote:
23)Which of the following statements must be true->
1)A prime number must be positive.
2)For any prime number p,there is no x such that 1<x<p and x is a divisor of p.
3)The product of first ten primes is even.
4)All prime numbers greater than 71 are odd.
5)2 and 3 are the only consecutive integers that are also prime numbers.
6)p is a prime number and x and y are positive integers.If p=x*y then one out of x or y must be one.
7)All the prime numbers greater than 3 can be written as either 4n+1 or 4n-1.
8)All the prime numbers greater than 3 can be written as either 6+1 or 6n-1.
Spoiler: ::
All statements are true.