What it shows
Type a whole number to find out whether it is prime (it has exactly two divisors, 1 and itself) or composite. For a composite number you get its prime factorisation, such as 360 = 2³ × 3² × 5, a list of all its divisors and their sum, and the nearest prime below and above it. The number 1 is neither prime nor composite, and 2 is the only even prime.
The second box takes two or more numbers and returns their greatest common divisor (GCD), the largest number that divides all of them, and their least common multiple (LCM), the smallest number that all of them divide. The GCD is used to simplify fractions and the LCM to find a common denominator.
Questions
How big a number can it handle? Up to 1,000,000,000,000,000 (10¹⁵). The page tests divisors up to the square root of the number, which takes a fraction of a second even at that size. Is it exact? Yes, only whole numbers are used. For fractions, see the Fraction Calculator; for other bases, the Number Base Converter.