The Fibonacci sequence:

1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

can be used to convert miles to kilometers (and vice versa). For example, to find how many km 5 miles is, take the next Fibonacci number which happens to be 8. Thus, 5 miles is approximately 8 km. Similarly, 8 miles is approximately 13 km, and so on.

This works because the growth rate of the Fibonacci numbers converges to the golden ratio (approx 1.618) which happens to be very close to the km/mile conversion (1 mile = 1.609 km).