Getting table at index results in nil even thought the index is used

[xtremsk8rs2]

I need to get a chunk in an array that does not start at 1, but when doing so, it throws up a nil even though the index is not nil.
I don’t know what this is called but getting the array values with pairs() works, I need to get a specific value here though.
I tried using tostring(i) to convert the index from a number to a string, as if it were a dictionary, but that also fails.

[xtremsk8rs2]

Apparently putting the indexes into tonumbers() fixes it. I would love to know why.

print(Chunks)
print(Chunks[tonumber(i)])
print(Chunks[tonumber(i)][tonumber(o)])
if Chunks[tonumber(i)][tonumber(o)][1]=="R" then
	local Level=Chunks[tonumber(i)][tonumber(o)][2]
	if Level>1 then
		chunk=Downscale(chunk,Level)
	end
end

EDIT: Apperently using pairs() gives a string index, while using ipairs() gives you an int index.