21987872 has 12 divisors (see below), whose sum is σ = 43288686. Its totient is φ = 10993920.

The previous prime is 21987871. The next prime is 21987899. The reversal of 21987872 is 27878912.

It can be written as a sum of positive squares in only one way, i.e., 20830096 + 1157776 = 4564^2 + 1076^2 .

It is not an unprimeable number, because it can be changed into a prime (21987871) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343529 + ... + 343592.

Almost surely, 2^21987872 is an apocalyptic number.

It is an amenable number.

21987872 is a deficient number, since it is larger than the sum of its proper divisors (21300814).

21987872 is an equidigital number, since it uses as much as digits as its factorization.

21987872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 687131 (or 687123 counting only the distinct ones).

The product of its digits is 112896, while the sum is 44.

The square root of 21987872 is about 4689.1227324522. The cubic root of 21987872 is about 280.1524340056.

The spelling of 21987872 in words is "twenty-one million, nine hundred eighty-seven thousand, eight hundred seventy-two".