21720897 has 24 divisors (see below), whose sum is σ = 34477248. Its totient is φ = 13068000.

The previous prime is 21720877. The next prime is 21720899. The reversal of 21720897 is 79802712.

It is not a de Polignac number, because 21720897 - 2⁶ = 21720833 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21720899) 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 23 ways as a sum of consecutive naturals, for example, 14223 + ... + 15675.

It is an arithmetic number, because the mean of its divisors is an integer number (1436552).

Almost surely, 2^21720897 is an apocalyptic number.

It is an amenable number.

21720897 is a deficient number, since it is larger than the sum of its proper divisors (12756351).

21720897 is a wasteful number, since it uses less digits than its factorization.

21720897 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1621 (or 1618 counting only the distinct ones).

The product of its (nonzero) digits is 14112, while the sum is 36.

The square root of 21720897 is about 4660.5683129850. The cubic root of 21720897 is about 279.0139508190.

The spelling of 21720897 in words is "twenty-one million, seven hundred twenty thousand, eight hundred ninety-seven".