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List primes, check divisibility, find GCD/LCM, and explore integer properties. Enter your number — see the complete number theory breakdown. Free.

Check divisibility rules for 2 through 13 with explanation. Enter your integer — see which divisors apply with the rule stated clearly. Free.

Convert numbers between any base 2 to 16. Fast and accurate result with formula, step-by-step method and unit overview. Free tool.

Check if a number is perfect, abundant, or deficient. Enter any positive integer — see divisor sum, classification, and factor list. Free.

Calculate Euler's Totient function φ(n) for any integer. Enter n — see the count of coprime integers, prime factorisation, and formula used. Free.

Find the sum of digits and digital root of any integer. Enter your number — see repeated digit sums until a single digit remains. Free.

Generate the Collatz sequence for any starting number. Enter n — see each step of the 3n+1 conjecture with total steps and peak value. Free.