21121864 has 16 divisors (see below), whose sum is σ = 39772800. Its totient is φ = 10515792.

The previous prime is 21121853. The next prime is 21121883. The reversal of 21121864 is 46812112.

It is a super-2 number, since 2×21121864² = 892266277668992, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3612 + ... + 7435.

It is an arithmetic number, because the mean of its divisors is an integer number (2485800).

Almost surely, 2^21121864 is an apocalyptic number.

It is an amenable number.

21121864 is a deficient number, since it is larger than the sum of its proper divisors (18650936).

21121864 is a wasteful number, since it uses less digits than its factorization.

21121864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11292 (or 11288 counting only the distinct ones).

The product of its digits is 768, while the sum is 25.

The square root of 21121864 is about 4595.8529132251. The cubic root of 21121864 is about 276.4250609239.

Adding to 21121864 its reverse (46812112), we get a palindrome (67933976).

The spelling of 21121864 in words is "twenty-one million, one hundred twenty-one thousand, eight hundred sixty-four".