21011864 has 32 divisors (see below), whose sum is σ = 42696720. Its totient is φ = 9655296.

The previous prime is 21011843. The next prime is 21011869. The reversal of 21011864 is 46811012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21011869) 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, 4052 + ... + 7644.

Almost surely, 2^21011864 is an apocalyptic number.

It is an amenable number.

21011864 is an abundant number, since it is smaller than the sum of its proper divisors (21684856).

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

21011864 is a wasteful number, since it uses less digits than its factorization.

21011864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3659 (or 3655 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 23.

The square root of 21011864 is about 4583.8699807041. The cubic root of 21011864 is about 275.9443632165.

Adding to 21011864 its reverse (46811012), we get a palindrome (67822876).

The spelling of 21011864 in words is "twenty-one million, eleven thousand, eight hundred sixty-four".