21808431 has 12 divisors (see below), whose sum is σ = 31945680. Its totient is φ = 14333760.

The previous prime is 21808417. The next prime is 21808441. The reversal of 21808431 is 13480812.

It is not a de Polignac number, because 21808431 - 2²² = 17614127 is a prime.

It is a super-2 number, since 2×21808431² = 951215325363522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21808395 and 21808404.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21808411) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 16426 + ... + 17703.

It is an arithmetic number, because the mean of its divisors is an integer number (2662140).

Almost surely, 2^21808431 is an apocalyptic number.

21808431 is a deficient number, since it is larger than the sum of its proper divisors (10137249).

21808431 is a wasteful number, since it uses less digits than its factorization.

21808431 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34206 (or 34203 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 27.

The square root of 21808431 is about 4669.9497855973. The cubic root of 21808431 is about 279.3882520027.

The spelling of 21808431 in words is "twenty-one million, eight hundred eight thousand, four hundred thirty-one".