21720268 has 24 divisors (see below), whose sum is σ = 40219200. Its totient is φ = 10235088.

The previous prime is 21720247. The next prime is 21720277. The reversal of 21720268 is 86202712.

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 16623 + ... + 17881.

It is an arithmetic number, because the mean of its divisors is an integer number (1675800).

Almost surely, 2^21720268 is an apocalyptic number.

It is an amenable number.

21720268 is a deficient number, since it is larger than the sum of its proper divisors (18498932).

21720268 is a wasteful number, since it uses less digits than its factorization.

21720268 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1509 (or 1507 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 28.

The square root of 21720268 is about 4660.5008314558. The cubic root of 21720268 is about 279.0112575375.

The spelling of 21720268 in words is "twenty-one million, seven hundred twenty thousand, two hundred sixty-eight".