21128664 has 16 divisors (see below), whose sum is σ = 52821720. Its totient is φ = 7042880.

The previous prime is 21128659. The next prime is 21128683. The reversal of 21128664 is 46682112.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

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, 440157 + ... + 440204.

Almost surely, 2^21128664 is an apocalyptic number.

21128664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21128664 is an abundant number, since it is smaller than the sum of its proper divisors (31693056).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21128664 is a wasteful number, since it uses less digits than its factorization.

21128664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 880370 (or 880366 counting only the distinct ones).

The product of its digits is 4608, while the sum is 30.

The square root of 21128664 is about 4596.5926510841. The cubic root of 21128664 is about 276.4547219540.

The spelling of 21128664 in words is "twenty-one million, one hundred twenty-eight thousand, six hundred sixty-four".