21523831 has 12 divisors (see below), whose sum is σ = 24983472. Its totient is φ = 18164736.

The previous prime is 21523813. The next prime is 21523847. The reversal of 21523831 is 13832512.

It is not a de Polignac number, because 21523831 - 2¹³ = 21515639 is a prime.

It is a super-2 number, since 2×21523831² = 926550601833122, 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 = 21523796 and 21523805.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21523891) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 37015 + ... + 37591.

It is an arithmetic number, because the mean of its divisors is an integer number (2081956).

Almost surely, 2^21523831 is an apocalyptic number.

21523831 is a deficient number, since it is larger than the sum of its proper divisors (3459641).

21523831 is an frugal number, since it uses more digits than its factorization.

21523831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 730 (or 657 counting only the distinct ones).

The product of its digits is 1440, while the sum is 25.

The square root of 21523831 is about 4639.3782988672. The cubic root of 21523831 is about 278.1675878226.

The spelling of 21523831 in words is "twenty-one million, five hundred twenty-three thousand, eight hundred thirty-one".