21903721 has 4 divisors (see below), whose sum is σ = 25032832. Its totient is φ = 18774612.

The previous prime is 21903719. The next prime is 21903733. The reversal of 21903721 is 12730912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21903721 - 2¹ = 21903719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21903781) 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 3 ways as a sum of consecutive naturals, for example, 1564545 + ... + 1564558.

It is an arithmetic number, because the mean of its divisors is an integer number (6258208).

Almost surely, 2^21903721 is an apocalyptic number.

It is an amenable number.

21903721 is a deficient number, since it is larger than the sum of its proper divisors (3129111).

21903721 is an equidigital number, since it uses as much as digits as its factorization.

21903721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3129110.

The product of its (nonzero) digits is 756, while the sum is 25.

The square root of 21903721 is about 4680.1411303507. The cubic root of 21903721 is about 279.7945814770.

The spelling of 21903721 in words is "twenty-one million, nine hundred three thousand, seven hundred twenty-one".