The 55th Fibonacci number is $139,583,862,445$.

Would you like more details or have any questions? Here are some related questions to deepen understanding:

1. What is the general formula for the Fibonacci sequence?
2. How does the Fibonacci sequence relate to the golden ratio?
3. Can the Fibonacci sequence be represented using matrices?
4. How do Fibonacci numbers appear in nature and geometry?
5. How can the Fibonacci sequence be used to solve real-world problems?

Tip: Fibonacci numbers grow exponentially as their index increases, approximately following the golden ratio $\phi \approx 1.618$.