21731808 has 96 divisors (see below), whose sum is σ = 66237696. Its totient is φ = 6110208.

The previous prime is 21731791. The next prime is 21731833. The reversal of 21731808 is 80813712.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (96).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 48835 + ... + 49277.

It is an arithmetic number, because the mean of its divisors is an integer number (689976).

Almost surely, 2^21731808 is an apocalyptic number.

21731808 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21731808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33118848).

21731808 is an abundant number, since it is smaller than the sum of its proper divisors (44505888).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21731808 is a wasteful number, since it uses less digits than its factorization.

21731808 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 536 (or 528 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 30.

The square root of 21731808 is about 4661.7387314177. The cubic root of 21731808 is about 279.0606617752.

The spelling of 21731808 in words is "twenty-one million, seven hundred thirty-one thousand, eight hundred eight".