21765720 has 64 divisors (see below), whose sum is σ = 67415040. Its totient is φ = 5616000.

The previous prime is 21765719. The next prime is 21765743. The reversal of 21765720 is 2756712.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 795 + ... + 6645.

It is an arithmetic number, because the mean of its divisors is an integer number (1053360).

Almost surely, 2^21765720 is an apocalyptic number.

21765720 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 21765720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33707520).

21765720 is an abundant number, since it is smaller than the sum of its proper divisors (45649320).

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

21765720 is a wasteful number, since it uses less digits than its factorization.

21765720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5896 (or 5892 counting only the distinct ones).

The product of its (nonzero) digits is 5880, while the sum is 30.

The square root of 21765720 is about 4665.3745830319. The cubic root of 21765720 is about 279.2057423088.

The spelling of 21765720 in words is "twenty-one million, seven hundred sixty-five thousand, seven hundred twenty".