21987439 has 4 divisors (see below), whose sum is σ = 22523760. Its totient is φ = 21451120.

The previous prime is 21987403. The next prime is 21987461. The reversal of 21987439 is 93478912.

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

It is a cyclic number.

It is not a de Polignac number, because 21987439 - 2¹³ = 21979247 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21987395 and 21987404.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987479) 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 3 ways as a sum of consecutive naturals, for example, 268099 + ... + 268180.

It is an arithmetic number, because the mean of its divisors is an integer number (5630940).

Almost surely, 2^21987439 is an apocalyptic number.

21987439 is a deficient number, since it is larger than the sum of its proper divisors (536321).

21987439 is an equidigital number, since it uses as much as digits as its factorization.

21987439 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 536320.

The product of its digits is 108864, while the sum is 43.

The square root of 21987439 is about 4689.0765615417. The cubic root of 21987439 is about 280.1505950100.

The spelling of 21987439 in words is "twenty-one million, nine hundred eighty-seven thousand, four hundred thirty-nine".