How can I identify prime numbers easily?

1 Answer
Apr 8, 2016

There is no easy way with large numbers.

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But you can exclude a lot of numbers by using the divisability rules:
- if it's even it's not a prime (only 2 is a prime)
- if the digits add up to a multiple of three, it's not a prime
- if it ends in 5 it's not a prime
And so on.