Spiral primes is a problem in which one must find the side length of the square spiral for which the ratio of primes along both diagonals first falls below 1...
Square root convergents is a problem in which one must find how many fractions of the square root of 2 contain a numerator with more digits than denominator.
Powerful digit sum is a problem in which one must find the maximum digital sum considering natural numbers of the form, a^b, where a, b < 100.
Lychrel numbers is a problem in which one must find how many Lychrel numbers are there below ten-thousand. You can read here more about Lychrel numbers.
If you’re trying to run Vaadin by following this and using Eclipse 4.4.1 it is likely that you will get the following error message: