21939731 has 4 divisors (see below), whose sum is σ = 23934264. Its totient is φ = 19945200.

The previous prime is 21939727. The next prime is 21939733. The reversal of 21939731 is 13793912.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21939731 - 2² = 21939727 is a prime.

It is a super-2 number, since 2×21939731² = 962703592704722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21939691 and 21939700.

It is not an unprimeable number, because it can be changed into a prime (21939733) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 997250 + ... + 997271.

It is an arithmetic number, because the mean of its divisors is an integer number (5983566).

Almost surely, 2^21939731 is an apocalyptic number.

21939731 is a deficient number, since it is larger than the sum of its proper divisors (1994533).

21939731 is a wasteful number, since it uses less digits than its factorization.

21939731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1994532.

The product of its digits is 10206, while the sum is 35.

The square root of 21939731 is about 4683.9866566847. The cubic root of 21939731 is about 279.9478261631.

The spelling of 21939731 in words is "twenty-one million, nine hundred thirty-nine thousand, seven hundred thirty-one".