Let a fun number be a positive integer of the form 4x+1. Then, the fun numbers are 1, 5, 9, 13, 17, 21, 25, 29, 33, 37... Let a fun prime be a fun number that is not divisible by any fun number other than 1 and itself. For example, 5 is a fun prime. Also, even though 9=3*3, 9 is a fun prime because 3 is not a fun number. Now, every fun number can be factored into fun primes. For example, 25=5*5. Find the first fun number with more than one fun prime factorization.

441 = 21 * 21 = 9 * 49

Posted by chun on 2017-11-14 12:22:53