https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
Mentioned: https://labs.spotify.com/2014/02/28/how-to-shuffle-songs/
Compute greatest common divisor: https://en.wikipedia.org/wiki/Euclidean_algorithm
Distance 2 ponits over surface earth: http://www.movable-type.co.uk/scripts/latlong.html