21209128 has 32 divisors (see below), whose sum is σ = 42091200. Its totient is φ = 9998208.

The previous prime is 21209119. The next prime is 21209129. The reversal of 21209128 is 82190212.

It is a super-2 number, since 2×21209128² = 899654221040768, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21209129) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12643 + ... + 14221.

It is an arithmetic number, because the mean of its divisors is an integer number (1315350).

Almost surely, 2^21209128 is an apocalyptic number.

It is an amenable number.

21209128 is a deficient number, since it is larger than the sum of its proper divisors (20882072).

21209128 is a wasteful number, since it uses less digits than its factorization.

21209128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1681 (or 1677 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 21209128 is about 4605.3369040712. The cubic root of 21209128 is about 276.8052169710.

The spelling of 21209128 in words is "twenty-one million, two hundred nine thousand, one hundred twenty-eight".