Is 1881 prime or composite

Answer 1

Composite, 1881 divided by 3 equals 627.

1881 is divisible by 9 as well. You can determine this by adding up the digits:

1 + 8 + 8 + 1 = 18 (which is divisible by 9, so the original number is divisible by 9).

This trick works to determine if a number is divisible by 3 as well (if the sum of digits is divisible by 3, then the number is divisible by 3).

Since 1881 has factors of 1881, 1, 9 and (1881 / 9 = 209) and you can stop there; you have determined that the number is not prime. {By the way, 11 & 19 are also factors}

Every number has factors of itself and 1. If it has other factors beside that, then it is composite. If those are the only 2 factors, then the number is prime.

If a number X is divisible by another number M, then M is a factor of X.