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By the fact that it is a Prime number, it does NOT factorise, except for itself and '1'.

They named prime numbers because they do factorise.

NB Except for '2' all prime numbers are odd numbers.

However, NOT all odd numbers are prime number.

Odd numbers ending in 1,3,7,& 9. can be prime numbers. Odd numbers ending in '5' are NOT prime number

So to test for a prime number.

If it is EVEN , ending in 0,2,4,6,8 , it is NOT a Prime Number.

It is ends in '5' it is NOT a prime Number.

If the digits sum to '9' it is NOT a Prime Number. e.g. 531 ; 5 + 3 + 1 = 9

So 531/ 9 = 59 So it is NOT a Prime number.

Then divide the given number by '3' or '7', if there isa remainder then it is a prime number.

So 1253

Try '3' = 417 remainder '2'

Try '7' =179 So 1253 is NOT a prime number.

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lenpollock

Lvl 17
1w ago

What else can I help you with?