21805920 has 144 divisors (see below), whose sum is σ = 78427440. Its totient is φ = 5501952.

The previous prime is 21805907. The next prime is 21805933. The reversal of 21805920 is 2950812.

It is an interprime number because it is at equal distance from previous prime (21805907) and next prime (21805933).

It is a tau number, because it is divible by the number of its divisors (144).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 26962 + ... + 27758.

It is an arithmetic number, because the mean of its divisors is an integer number (544635).

Almost surely, 2^21805920 is an apocalyptic number.

21805920 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 21805920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39213720).

21805920 is an abundant number, since it is smaller than the sum of its proper divisors (56621520).

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

21805920 is a wasteful number, since it uses less digits than its factorization.

21805920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 837 (or 826 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 27.

The square root of 21805920 is about 4669.6809312843. The cubic root of 21805920 is about 279.3775287671.

It can be divided in two parts, 2180 and 5920, that added together give a square (8100 = 90²).

The spelling of 21805920 in words is "twenty-one million, eight hundred five thousand, nine hundred twenty".