21708720 has 120 divisors (see below), whose sum is σ = 79561872. Its totient is φ = 5260800.

The previous prime is 21708703. The next prime is 21708727. The reversal of 21708720 is 2780712.

It is a tau number, because it is divible by the number of its divisors (120).

It is not an unprimeable number, because it can be changed into a prime (21708727) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6550 + ... + 9290.

Almost surely, 2^21708720 is an apocalyptic number.

21708720 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 21708720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39780936).

21708720 is an abundant number, since it is smaller than the sum of its proper divisors (57853152).

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

21708720 is a wasteful number, since it uses less digits than its factorization.

21708720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2771 (or 2762 counting only the distinct ones).

The product of its (nonzero) digits is 1568, while the sum is 27.

The square root of 21708720 is about 4659.2617440964. The cubic root of 21708720 is about 278.9618015303.

The spelling of 21708720 in words is "twenty-one million, seven hundred eight thousand, seven hundred twenty".