21720903 has 4 divisors (see below), whose sum is σ = 28961208. Its totient is φ = 14480600.

The previous prime is 21720899. The next prime is 21720911. The reversal of 21720903 is 30902712.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21720903 - 2² = 21720899 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720953) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3620148 + ... + 3620153.

It is an arithmetic number, because the mean of its divisors is an integer number (7240302).

Almost surely, 2^21720903 is an apocalyptic number.

21720903 is a deficient number, since it is larger than the sum of its proper divisors (7240305).

21720903 is an equidigital number, since it uses as much as digits as its factorization.

21720903 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7240304.

The product of its (nonzero) digits is 756, while the sum is 24.

The square root of 21720903 is about 4660.5689566833. The cubic root of 21720903 is about 279.0139765098.

The spelling of 21720903 in words is "twenty-one million, seven hundred twenty thousand, nine hundred three".