Why primes above 3 give p squared minus 1 divisible by 24
Question
Let be any prime larger than . Explain why always divides .
Short answer
Factor . Since is odd, and are consecutive even numbers, one of them a multiple of , so divides the product. Among one is a multiple of and it is not , so divides the product too; hence does.
Adapted from Crack, Heard on the Street, Q1.49, p.19; question and answer rewritten by SelfMadeQuant.com.
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