Project Euler is a series of challenging problems that require mathematical and programming skills. Somebody who enjoys learning new area of mathematics, project Euler is going to be a fun journey.

All Problems of the Project Euler are available at: Project Euler

Fromula for n^th Fibonnaci Number
Binet's Formula-

Binet's formula is an explicit formula used to find the $n$th term of the Fibonacci sequence. It is so named because it was derived by mathematician Jacques Philippe Marie Binet, though it was already known by Abraham de Moivre.
Read about Binet's Formula at- Binet's Forumla