21715920 has 60 divisors (see below), whose sum is σ = 72931716. Its totient is φ = 5790720.

The previous prime is 21715913. The next prime is 21715921. The reversal of 21715920 is 2951712.

21715920 is a `hidden beast` number, since 2 + 1 + 71 + 592 + 0 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 12787776 + 8928144 = 3576^2 + 2988^2 .

It is a tau number, because it is divible by the number of its divisors (60).

It is a nialpdrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21715921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14361 + ... + 15800.

Almost surely, 2^21715920 is an apocalyptic number.

21715920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21715920 is an abundant number, since it is smaller than the sum of its proper divisors (51215796).

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

21715920 is a wasteful number, since it uses less digits than its factorization.

21715920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30180 (or 30171 counting only the distinct ones).

The product of its (nonzero) digits is 1260, while the sum is 27.

The square root of 21715920 is about 4660.0343346375. The cubic root of 21715920 is about 278.9926386465.

The spelling of 21715920 in words is "twenty-one million, seven hundred fifteen thousand, nine hundred twenty".