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156 is a not a prime number. A prime number is a number that only can divided by 1 and itself. Examples of Primes is 1, 2,3, 5, 7, 11, 13, 17.......................... 156 factors include 1,2,3,4,6,12,13,26,39,52,78,156. A easy way to figure out if a prime number is a prime number or not look and see if the last digit in the number. If the digit is even is it not a prime number.
There is no quick way to work out if a number is prime or not, the only way is to see if it can be divided by any numbers that aren't itself or one.
There is no easy way or really, any way at all to memorize an infinite list.
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126 63,2 21,3,2 7,3,3,2