21664603 has 4 divisors (see below), whose sum is σ = 22125600. Its totient is φ = 21203608.

The previous prime is 21664529. The next prime is 21664607. The reversal of 21664603 is 30646612.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21664603 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21664607) 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, 230428 + ... + 230521.

It is an arithmetic number, because the mean of its divisors is an integer number (5531400).

Almost surely, 2^21664603 is an apocalyptic number.

21664603 is a deficient number, since it is larger than the sum of its proper divisors (460997).

21664603 is an equidigital number, since it uses as much as digits as its factorization.

21664603 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 460996.

The product of its (nonzero) digits is 5184, while the sum is 28.

The square root of 21664603 is about 4654.5250026184. The cubic root of 21664603 is about 278.7727023410.

Subtracting 21664603 from its reverse (30646612), we obtain a square (8982009 = 2997²).

The spelling of 21664603 in words is "twenty-one million, six hundred sixty-four thousand, six hundred three".