21255731 has 4 divisors (see below), whose sum is σ = 24292272. Its totient is φ = 18219192.

The previous prime is 21255727. The next prime is 21255733. The reversal of 21255731 is 13755212.

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

It is a cyclic number.

It is not a de Polignac number, because 21255731 - 2² = 21255727 is a prime.

It is a super-2 number, since 2×21255731² = 903612200688722, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21255731.

It is not an unprimeable number, because it can be changed into a prime (21255733) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1518260 + ... + 1518273.

It is an arithmetic number, because the mean of its divisors is an integer number (6073068).

Almost surely, 2^21255731 is an apocalyptic number.

21255731 is a deficient number, since it is larger than the sum of its proper divisors (3036541).

21255731 is an equidigital number, since it uses as much as digits as its factorization.

21255731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3036540.

The product of its digits is 2100, while the sum is 26.

The square root of 21255731 is about 4610.3938009675. The cubic root of 21255731 is about 277.0078108203.

The spelling of 21255731 in words is "twenty-one million, two hundred fifty-five thousand, seven hundred thirty-one".