21718720 has 56 divisors (see below), whose sum is σ = 52541424. Its totient is φ = 8549376.

The previous prime is 21718703. The next prime is 21718721. The reversal of 21718720 is 2781712.

It is not an unprimeable number, because it can be changed into a prime (21718721) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 20934 + ... + 21946.

Almost surely, 2^21718720 is an apocalyptic number.

21718720 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 21718720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26270712).

21718720 is an abundant number, since it is smaller than the sum of its proper divisors (30822704).

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

21718720 is a wasteful number, since it uses less digits than its factorization.

21718720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1097 (or 1087 counting only the distinct ones).

The product of its (nonzero) digits is 1568, while the sum is 28.

The square root of 21718720 is about 4660.3347519250. The cubic root of 21718720 is about 279.0046290175.

The spelling of 21718720 in words is "twenty-one million, seven hundred eighteen thousand, seven hundred twenty".