What numbers are not prime numbers?

Answer 1

Any natural number with exactly two unique factors, 1 and itself, is a Prime number. Any other natural number is composite, not prime. So, some numbers that are not prime are 0, 1, negative numbers, fractions, decimals, Irrational Numbers, and imaginary numbers. Here are some numbers that are not prime numbers.

1/2

5/6

0.06

250

51

1.39

π

√2

3i

All integers greater than one (the natural numbers) that are not prime numbers are composite numbers. Composite numbers are integers that have more than two factors, including 1. Here is a list of some numbers and whether they are prime numbers or composite numbers.

1 - unity, neither prime nor composite

2 - prime

3 - prime

4 - composite (factors are 1, 2, and 4)

5 - prime

6 - composite (factors are 1, 2, 3, and 6)

7 - prime

8 - composite (factors are 1, 2, 4, and 8)

9 - composite (factors are 1, 3, and 9)

10 - composite (factors are 1, 2, 5, and 10)

___________________

Any natural number (of 2 or more digits, understood throughout this answer) that ends with 0, 2, 4, 5, 6 or 8 must be a composite number and therefore cannot be prime. Primes will end only with 1, 3, 7 or 9, but composite numbers can end with any digit.

Any number with a digital root* of 3, 6 or 9 must be a composite number and therefore cannot be prime. A prime number will have a digital root that equals 1, 2, 4, 5, 7 or 8, but composite numbers can have a digital root of any nonzero integer.

*The digital root of a number is the result of adding a number's digits, continuing to add the digits of the sum, until you are left with one single digit. You can add the digits in any order, and can add the digits of the accumulated sum at any time; the result will always be the same if done accurately.

Even if given a very long number that ends in 1, 3, 7 or 9, you might be able to stun people by accurately stating that the number must be composite, if you mentally calculate the digital root and find it to be 3, 6 or 9. You won't be able to isolate every single composite, but with a digital root of 3, 6, or 9, you can be certain that THAT number IS composite.

Any natural number divided by 6 is composite if the digital fraction is equal to .0 exactly, .5 exactly, .3333 repeating, or.6666 repeating.

Answer 2

Any number that can be evenly divided by another number.

All even numbers except 2, all numbers that can be divided by 3 except 3, all numbers that can be divided by 5 except 5, etc.

Ans 2.

One definition is a number with only one factor or more than two factors.

Answer 3

CONSECITIVE

Answer 4

5