Topic: Arithmetic
Question Source: PrepSwift
Question:
When given a large number like this, how can one determine whether it is prime or not prime? Is there a nimble way to determine whether the numbers are prime?
What I tried

I tried coming up with examples to see if there’s a rule like prime + composite = prime with numbers like 2 + 1 = 3. But, I saw counterexamples for this assumption like 3 + 1 = 4.

I also tried to list out 30! + x as (30 * 29 * 28 * … * 1) + x, and see if I can factor out the result algebraically. However, even that did not lead me to the right path.
If you can provide a nimbler approach, I hereby declare you the smartest GRE math whiz