21055720 has 64 divisors (see below), whose sum is σ = 54633600. Its totient is φ = 7153920.

The previous prime is 21055717. The next prime is 21055733. The reversal of 21055720 is 2755012.

It is a junction number, because it is equal to n+sod(n) for n = 21055691 and 21055700.

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, 38650 + ... + 39190.

It is an arithmetic number, because the mean of its divisors is an integer number (853650).

Almost surely, 2^21055720 is an apocalyptic number.

21055720 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 21055720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27316800).

21055720 is an abundant number, since it is smaller than the sum of its proper divisors (33577880).

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

21055720 is a wasteful number, since it uses less digits than its factorization.

21055720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 698 (or 694 counting only the distinct ones).

The product of its (nonzero) digits is 700, while the sum is 22.

The square root of 21055720 is about 4588.6512179507. The cubic root of 21055720 is about 276.1362136571.

The spelling of 21055720 in words is "twenty-one million, fifty-five thousand, seven hundred twenty".