21728831 has 2 divisors, whose sum is σ = 21728832. Its totient is φ = 21728830.

The previous prime is 21728827. The next prime is 21728843. The reversal of 21728831 is 13882712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21728831 - 2² = 21728827 is a prime.

It is a super-2 number, since 2×21728831² = 944284193253122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21728851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10864415 + 10864416.

It is an arithmetic number, because the mean of its divisors is an integer number (10864416).

Almost surely, 2^21728831 is an apocalyptic number.

21728831 is a deficient number, since it is larger than the sum of its proper divisors (1).

21728831 is an equidigital number, since it uses as much as digits as its factorization.

21728831 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5376, while the sum is 32.

The square root of 21728831 is about 4661.4194190182. The cubic root of 21728831 is about 279.0479185262.

The spelling of 21728831 in words is "twenty-one million, seven hundred twenty-eight thousand, eight hundred thirty-one".