21187872 has 96 divisors (see below), whose sum is σ = 62596800. Its totient is φ = 6971904.

The previous prime is 21187871. The next prime is 21187883. The reversal of 21187872 is 27878112.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (96).

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 (21187871) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 118279 + ... + 118457.

It is an arithmetic number, because the mean of its divisors is an integer number (652050).

Almost surely, 2^21187872 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21187872, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31298400).

21187872 is an abundant number, since it is smaller than the sum of its proper divisors (41408928).

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

21187872 is a wasteful number, since it uses less digits than its factorization.

21187872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 335 (or 321 counting only the distinct ones).

The product of its digits is 12544, while the sum is 36.

The square root of 21187872 is about 4603.0285682364. The cubic root of 21187872 is about 276.7127137434.

The spelling of 21187872 in words is "twenty-one million, one hundred eighty-seven thousand, eight hundred seventy-two".