21756720 has 80 divisors (see below), whose sum is σ = 67897440. Its totient is φ = 5763072.

The previous prime is 21756677. The next prime is 21756733. The reversal of 21756720 is 2765712.

It is a tau number, because it is divible by the number of its divisors (80).

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

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, 64392 + ... + 64728.

It is an arithmetic number, because the mean of its divisors is an integer number (848718).

Almost surely, 2^21756720 is an apocalyptic number.

21756720 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 21756720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33948720).

21756720 is an abundant number, since it is smaller than the sum of its proper divisors (46140720).

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

21756720 is a wasteful number, since it uses less digits than its factorization.

21756720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 622 (or 616 counting only the distinct ones).

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

The square root of 21756720 is about 4664.4099305271. The cubic root of 21756720 is about 279.1672536806.

The spelling of 21756720 in words is "twenty-one million, seven hundred fifty-six thousand, seven hundred twenty".