The Fibonacci sequence is a good approximation for the conversion between miles and kilometers.
1 mile = 1.6 km
2 miles = 3.21 km
3 miles = 4.82 km
5 miles = 8.04 km
8 miles = 12.87 km
13 miles = 20.92 km
You can generate the sequence on your own, by starting with two 1’s and then adding together the last two numbers to get the next. The ratio between numbers in the sequence converges the Golden Ratio, phi:
which is of course numerically very close to the actual conversion ratio of miles to kilometers, 1.609344.