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This simple isprime(number) function checks if the given integer number is a prime number and returns True or False. The function makes sure that the number is a positive integer, and that 1 is not considered a prime number.

To find out if an integer n is odd one can use `n & 1`

, to check for even one can then use `not n & 1`

or the more traditional `n % 2 == 0`

which is about 30% slower.