21401864 has 16 divisors (see below), whose sum is σ = 43776720. Its totient is φ = 9728080.

The previous prime is 21401857. The next prime is 21401867. The reversal of 21401864 is 46810412.

It is not an unprimeable number, because it can be changed into a prime (21401867) 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, 121514 + ... + 121689.

It is an arithmetic number, because the mean of its divisors is an integer number (2736045).

Almost surely, 2^21401864 is an apocalyptic number.

It is an amenable number.

21401864 is an abundant number, since it is smaller than the sum of its proper divisors (22374856).

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

21401864 is a wasteful number, since it uses less digits than its factorization.

21401864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 243220 (or 243216 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 26.

The square root of 21401864 is about 4626.2148674699. The cubic root of 21401864 is about 277.6411704946.

It can be divided in two parts, 2140 and 1864, that added together give a palindrome (4004).

The spelling of 21401864 in words is "twenty-one million, four hundred one thousand, eight hundred sixty-four".