21987039 has 4 divisors (see below), whose sum is σ = 29316056. Its totient is φ = 14658024.

The previous prime is 21987019. The next prime is 21987041. The reversal of 21987039 is 93078912.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21987039 - 2¹⁹ = 21462751 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21986988 and 21987006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987019) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3664504 + ... + 3664509.

It is an arithmetic number, because the mean of its divisors is an integer number (7329014).

Almost surely, 2^21987039 is an apocalyptic number.

21987039 is a deficient number, since it is larger than the sum of its proper divisors (7329017).

21987039 is an equidigital number, since it uses as much as digits as its factorization.

21987039 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7329016.

The product of its (nonzero) digits is 27216, while the sum is 39.

The square root of 21987039 is about 4689.0339090265. The cubic root of 21987039 is about 280.1488961473.

The spelling of 21987039 in words is "twenty-one million, nine hundred eighty-seven thousand, thirty-nine".