If the number fits in an 8 bit byte, then prepend 0s to make full 8 bit bytes, numbers above 255 get new digits added (like normal binary)

gistfile1.lua

function DecToBase(IN,BASE)
    local B,K,OUT,D=BASE or 10,"0123456789ABCDEFGHIJKLMNOPQRSTUVW",""
    while IN>0 do
        IN,D=math.floor(IN/B),math.mod(IN,B)+1
        OUT=string.sub(K,D,D)..OUT
    end
	if string.len(OUT) == 1 then
		OUT = "0000000" .. OUT
	elseif string.len(OUT) == 2 then
		OUT = "000000" .. OUT
	elseif string.len(OUT) == 3 then
		OUT = "00000" .. OUT
	elseif string.len(OUT) == 4 then
		OUT = "0000" .. OUT
	elseif string.len(OUT) == 5 then
		OUT = "000" .. OUT
	elseif string.len(OUT) == 6 then
		OUT = "00" .. OUT
	elseif string.len(OUT) == 7 then
		OUT = "0" .. OUT
	elseif string.len(OUT) == 8 then
		OUT = OUT
	else
		OUT = OUT
	end
	
    return OUT
end
print 'What is your number?'

number = io.read()

number = tonumber(number)

print (DecToBase(number,2))