/gamerule spawnRadius [number] keeps any number in his memory

If you put a set of number with spaces in it, the gamerule will only count the first number (which is obviously intended) and will keep all numbers that has been entered in the command.

/gamerule spawnRadius 0 1 2 3 4

Then do,

/gamerule spawnRadius

and it will return "spawnRadius = 0 1 2 3 4"