At the 1912 International Congress of Mathematicians, Edmund Landau listed four basic problems about primes. These problems were characterised in his speech as "unattackable at the present state of science" and are now known as Landau's problems. They are as follows:
- Goldbach's conjecture: Can every even integer greater than 2 be written as the sum of two primes?
- Twin prime conjecture: Are there infinitely many primes p such that p + 2 is prime?
- Legendre's conjecture: Does there always exist at least one prime between consecutive perfect squares?
- Are there infinitely many primes p such that p − 1 is a perfect square? In other words: Are there infinitely many primes of the form n2 + 1? (sequence A002496 in OEIS).
As of 2012, all four problems are unresolved.
Famous quotes containing the word problems:
“I’m no good at being noble, but it doesn’t take much to see that the problems of three little people don’t amount to a hill of beans in this crazy world. Someday you’ll understand that.”
—Julius J. Epstein, U.S. screenwriter, Philip Epstein, screenwriter, Howard Koch, screenwriter, and Michael Curtiz. Rick Blaine (Humphrey Bogart)