21731868 has 48 divisors (see below), whose sum is σ = 58168320. Its totient is φ = 7009200.

The previous prime is 21731863. The next prime is 21731869. The reversal of 21731868 is 86813712.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21731861) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 103 + ... + 6593.

It is an arithmetic number, because the mean of its divisors is an integer number (1211840).

Almost surely, 2^21731868 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21731868, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29084160).

21731868 is an abundant number, since it is smaller than the sum of its proper divisors (36436452).

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

21731868 is a wasteful number, since it uses less digits than its factorization.

21731868 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6535 (or 6527 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 21731868 is about 4661.7451667804. The cubic root of 21731868 is about 279.0609185973.

The spelling of 21731868 in words is "twenty-one million, seven hundred thirty-one thousand, eight hundred sixty-eight".