A member of the sequence of numbers such that each number is the sum of the preceding two. The first seven numbers are 1, 1, 2, 3, 5, 8, and 13. F(n) ≈ round(Φⁿ/√ 5), where Φ=(1+√ 5)/2. Formal Definition: The n^th Fibonacci number is

• F(n) = F(n-1) + F(n-2), where F(1)=1 and F(2)=1, or
• F(n) = (Φⁿ - φⁿ)/√ 5, where Φ=(1+√ 5)/2 and φ=(1-√ 5)/2.