Erdos and Selfridge developed a scheme for classifying a prime number p: If the only factors of p+1 are 2 and 3, then put p in class 1. Otherwise, find the largest class r of the factors of p+1 and put p in class r+1.
For example, 11 is in class 1 because 12 has prime factors 2, 2, and 3. The number 43 is in class 2 because 44 has prime factors 2, 2, and 11, and all of those are in class 1. All Mersenne primes are in class 1, and all ugly numbers are in classes 1 or 2.
Write a function to classify prime numbers using this scheme.
Solve

Solution Stats

26 Solutions

16 Solvers

Last Solution submitted on Jul 20, 2026

Last 200 Solutions

Problem Comments

Solution Comments

Show comments

Problem Recent Solvers16

Chris Cleveland George Berken Mehdi Dehghan Lorenzo

Suggested Problems

More from this Author329

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!