[Doctor Stochastic]

The four-color problem was solved in 1977; four suffice.

The biggest remaining problem is the Riemann Hypothesis.

There are others, the Goldbach hypothesis, the infinitude of twin primes, some stuff from Poincare (I don't remember the details), and there will be more in the future.

[general_re]

Well, there you go - and I was worried there'd be nothing left for me ;)

[longshadow]

The biggest remaining problem is the Riemann Hypothesis.

Worth noting that Hilbert chose to include this among his famous 23 unsolved problems.

"Wir müssen wissen, wir werden wissen." -David Hilbert