If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.

Problem 2:

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …
Find the sum of all the even-valued terms in the sequence which do not exceed four million.

Problem 3:

The prime factors of 13195 are 5, 7, 13 and 29.
What is the largest prime factor of the number 600851475143?

2. If you are into numerical analysis, you may try Newton Basin Fractal, i.e. finding roos of a polynomical function in a complex plane, you can be inspired by Jonathan Birge did:

Can anyone help me to find out how many times a sequence number (like twice 2,2 or thrice 2,2,2 or four times 2,2,2,2) are repeated in any programming language?

1,1,2,3,4,5,6,2,2,2,5,3,3,2,2,1,5,5,5,5,4,4,4,1,2,2,2,2,6,6,2,2,1,1,2,2

Can anyone help me to find out how many times a sequence number (like twice 2,2 or thrice 2,2,2 or four times 2,2,2,2) are repeated in any programming language?