You'll have to test whether 1823 can be divided by every number from 2 up to 42. You can stop there because 43 x 43 is bigger than 1823. You can test only prime numbers between 2 and 42, so 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41. 2 is out because 1823 is not even. 3 is out because 1 + 8 + 2 + 3 is 14, which does not divide by 3. 5 is out because 1823 does not end in 0 or 5. 7 is out because 182 - 3x2 = 176, which does not divide by 7. 11 is out because 182 - 3x1 = 179, which does not divide by 11. Then I run out of tricks to see if numbers can be divided by other numbers, so I test with a calculator. Everything gives a fraction. So 1823 is prime.
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neither prime or composite
It is prime
It would be impossible to list them all, since numbers go on forever, but here are some of them: 2 - Prime 3 - Prime 4 - Composite 5 - Prime 6 - Composite 7 - Prime 8 - Composite 9 - Composite 10 - Composite 11 - Prime 12 - Composite 13 - Prime 14 - Composite 15 - Composite 16 - Composite 17 - Prime 18 - Composite 19 - Prime 20 - Composite 21 - Composite 22 - Composite 23 - Prime 24 - Composite 25 - Composite 26 - Composite 27 - Composite 28 - Composite 29 - Prime 30 - Composite 31 - Prime 32 - Composite 33 - Composite 34 - Composite 35 - Composite 36 - Composite 37 - Prime 38 - Composite 39 - Composite 40 - Composite 41 - Prime 42 - Composite 43 - Prime 44 - Composite 45 - Composite 46 - Composite 47 - Prime 48 - Composite 49 - Composite 50 - Composite
composite
is 71 a prime or a composite