21664503 has 40 divisors (see below), whose sum is σ = 38952320. Its totient is φ = 11722320.

The previous prime is 21664501. The next prime is 21664507. The reversal of 21664503 is 30546612.

21664503 is a `hidden beast` number, since 2 + 16 + 645 + 0 + 3 = 666.

It is not a de Polignac number, because 21664503 - 2¹ = 21664501 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664501) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 9768 + ... + 11778.

It is an arithmetic number, because the mean of its divisors is an integer number (973808).

Almost surely, 2^21664503 is an apocalyptic number.

21664503 is a deficient number, since it is larger than the sum of its proper divisors (17287817).

21664503 is a wasteful number, since it uses less digits than its factorization.

21664503 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2049 (or 2040 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 21664503 is about 4654.5142603713. The cubic root of 21664503 is about 278.7722734184.

The spelling of 21664503 in words is "twenty-one million, six hundred sixty-four thousand, five hundred three".