What is the greatest prime to consider weather to test 1881 is prime.

the greates prime to consider is?

2 answers

can it divide by 123456789?
it can divide by 9
hope that answered your question!
When testing if a number is prime, you would only try primes as divisors until you reach the last prime < √(the number)
e.g. is 71 prime
try: 2, 3, 5, 7
none divided exactly, so 71 is prime
(did not have to go for 11 , since 11 > √71

so for 1881 ...
√1881 = 43.37..
and since 43 is prime, that would be the greatest prime I would consider.
HOWEVER, 1881 divides evenly by 11 , which is prime.
So one interpretation of your question would have the answer as 11

But, they way it is worded, 43 would be greatest prime one would consider in testing if 1881 is prime.