This is neat. (Mentioned by a friend of a friend.)

Problem, Description, Solved By how many people

1 Add all the natural numbers below one thousand that are multiples of 3 or 5. 41094

2 Find the sum of all the even-valued terms in the Fibonacci sequence which do not exceed four million. 34131

3 Find the largest prime factor of a composite number. 24864

4 Find the largest palindrome made from the product of two 3-digit numbers. 23312

5 What is the smallest number divisible by each of the numbers 1 to 20? 27040

6 What is the difference between the sum of the squares and the square of the sums? 27723

7 Find the 10001st prime. 23039

8 Discover the largest product of five consecutive digits in the 1000-digit number. 20894

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