Here's a fun TIL: Because the ratio of terms in the Fibonacci sequence approaches phi, and because phi is close to the ratio of km to miles, you can approximate conversion between distances with adjacent Fibonacci numbers.
So 2 km ≈ 1 mile, 3 km ≈ 2 miles, 5 km ≈ 3 miles, 8 km ≈ 5 miles, 13 km ≈ 8 miles, etc, etc