21978252 has 36 divisors (see below), whose sum is σ = 56609280. Its totient is φ = 7187232.

The previous prime is 21978251. The next prime is 21978293. The reversal of 21978252 is 25287912.

It is a tau number, because it is divible by the number of its divisors (36).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (21978251) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3852 + ... + 7667.

It is an arithmetic number, because the mean of its divisors is an integer number (1572480).

Almost surely, 2^21978252 is an apocalyptic number.

It is an amenable number.

21978252 is an abundant number, since it is smaller than the sum of its proper divisors (34631028).

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

21978252 is a wasteful number, since it uses less digits than its factorization.

21978252 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11582 (or 11577 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 21978252 is about 4688.0968420032. The cubic root of 21978252 is about 280.1115711828. Note that the first 3 decimals are identical.

The spelling of 21978252 in words is "twenty-one million, nine hundred seventy-eight thousand, two hundred fifty-two".