21056731 has 8 divisors (see below), whose sum is σ = 22211280. Its totient is φ = 19906848.

The previous prime is 21056723. The next prime is 21056743. The reversal of 21056731 is 13765012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21056731 - 2³ = 21056723 is a prime.

It is a super-2 number, since 2×21056731² = 886771840812722, 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 = 21056696 and 21056705.

It is not an unprimeable number, because it can be changed into a prime (21056701) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12045 + ... + 13681.

It is an arithmetic number, because the mean of its divisors is an integer number (2776410).

Almost surely, 2^21056731 is an apocalyptic number.

21056731 is a deficient number, since it is larger than the sum of its proper divisors (1154549).

21056731 is a wasteful number, since it uses less digits than its factorization.

21056731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2333.

The product of its (nonzero) digits is 1260, while the sum is 25.

The square root of 21056731 is about 4588.7613797189. The cubic root of 21056731 is about 276.1406331884.

It can be divided in two parts, 2105 and 6731, that added together give a square (8836 = 94²).

The spelling of 21056731 in words is "twenty-one million, fifty-six thousand, seven hundred thirty-one".