How to find when a variable is a decimal?

So I am making a script that tells me what number is a prime number.

local dividend= 1
local divisor= 1


function divide()
	local result= dividend/divisor
	--if result is not a decimal then
		--if result is not 1 or "dividend" then
	print(dividend.."is not a prime number")
	else
		print(dividend.."is a prime number")
		dividend= dividend + 1
		divisor= 1
	end
end
divisor= divisor + 1
end

while true do
	divide()
wait()
end

In line 7, I don't know how to find if "result" has a decimal, as per the question says. In line 8, as soon as I type "not", it gets a red line under it.

Please note that I put the end and else just for convenience so please don't tell me that's the one incorrect.