21664903 has 4 divisors (see below), whose sum is σ = 23331448. Its totient is φ = 19998360.

The previous prime is 21664897. The next prime is 21664967. The reversal of 21664903 is 30946612.

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 21664903 - 2¹³ = 21656711 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664703) 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 3 ways as a sum of consecutive naturals, for example, 833253 + ... + 833278.

It is an arithmetic number, because the mean of its divisors is an integer number (5832862).

Almost surely, 2^21664903 is an apocalyptic number.

21664903 is a deficient number, since it is larger than the sum of its proper divisors (1666545).

21664903 is a wasteful number, since it uses less digits than its factorization.

21664903 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1666544.

The product of its (nonzero) digits is 7776, while the sum is 31.

The square root of 21664903 is about 4654.5572292110. The cubic root of 21664903 is about 278.7739891009.

The spelling of 21664903 in words is "twenty-one million, six hundred sixty-four thousand, nine hundred three".