21128207 has 4 divisors (see below), whose sum is σ = 21219120. Its totient is φ = 21037296.

The previous prime is 21128203. The next prime is 21128213. The reversal of 21128207 is 70282112.

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 21128207 - 2² = 21128203 is a prime.

It is a super-2 number, since 2×21128207² = 892802262069698, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21128201) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 45107 + ... + 45572.

It is an arithmetic number, because the mean of its divisors is an integer number (5304780).

Almost surely, 2^21128207 is an apocalyptic number.

21128207 is a deficient number, since it is larger than the sum of its proper divisors (90913).

21128207 is an equidigital number, since it uses as much as digits as its factorization.

21128207 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 90912.

The product of its (nonzero) digits is 448, while the sum is 23.

The square root of 21128207 is about 4596.5429400801. The cubic root of 21128207 is about 276.4527287578.

The spelling of 21128207 in words is "twenty-one million, one hundred twenty-eight thousand, two hundred seven".