Try Project Euler

• en) https://projecteuler.net/
• ja) http://odz.sakura.ne.jp/projecteuler/

Language

• Haskell
• Go
• C++
• Ruby

Problems

• 1 Multiples of 3 and 5
• 2 Even Fibonacci numbers
• 3 Largest prime factor
• 4 Largest palindrome product
• 5 Smallest multiple
• 6 Sum square difference
• 7 10001st prime
• [] 8 Largest product in a series
• [] 9 Special Pythagorean triplet
• [] 10 Summation of primes