21385831 has 4 divisors (see below), whose sum is σ = 21421000. Its totient is φ = 21350664.

The previous prime is 21385823. The next prime is 21385843. The reversal of 21385831 is 13858312.

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 21385831 - 2³ = 21385823 is a prime.

It is a super-2 number, since 2×21385831² = 914707535121122, 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 = 21385793 and 21385802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21385801) 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, 16656 + ... + 17893.

It is an arithmetic number, because the mean of its divisors is an integer number (5355250).

Almost surely, 2^21385831 is an apocalyptic number.

21385831 is a deficient number, since it is larger than the sum of its proper divisors (35169).

21385831 is an equidigital number, since it uses as much as digits as its factorization.

21385831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35168.

The product of its digits is 5760, while the sum is 31.

The square root of 21385831 is about 4624.4817006882. The cubic root of 21385831 is about 277.5718224396.

The spelling of 21385831 in words is "twenty-one million, three hundred eighty-five thousand, eight hundred thirty-one".