21231840 has 192 divisors, whose sum is σ = 78382080. Its totient is φ = 4730880.

The previous prime is 21231823. The next prime is 21231841. The reversal of 21231840 is 4813212.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21231841) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 238516 + ... + 238604.

It is an arithmetic number, because the mean of its divisors is an integer number (408240).

Almost surely, 2^21231840 is an apocalyptic number.

21231840 is a gapful number since it is divisible by the number (20) 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 21231840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39191040).

21231840 is an abundant number, since it is smaller than the sum of its proper divisors (57150240).

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

21231840 is a wasteful number, since it uses less digits than its factorization.

21231840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 185 (or 177 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 21.

The square root of 21231840 is about 4607.8020790828. The cubic root of 21231840 is about 276.9039882379.

The spelling of 21231840 in words is "twenty-one million, two hundred thirty-one thousand, eight hundred forty".