21857439 has 4 divisors (see below), whose sum is σ = 29143256. Its totient is φ = 14571624.

The previous prime is 21857431. The next prime is 21857447. The reversal of 21857439 is 93475812.

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

It is an interprime number because it is at equal distance from previous prime (21857431) and next prime (21857447).

It is not a de Polignac number, because 21857439 - 2³ = 21857431 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21857397 and 21857406.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21857431) 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, 3642904 + ... + 3642909.

It is an arithmetic number, because the mean of its divisors is an integer number (7285814).

Almost surely, 2^21857439 is an apocalyptic number.

21857439 is a deficient number, since it is larger than the sum of its proper divisors (7285817).

21857439 is an equidigital number, since it uses as much as digits as its factorization.

21857439 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7285816.

The product of its digits is 60480, while the sum is 39.

The square root of 21857439 is about 4675.1940066697. The cubic root of 21857439 is about 279.5973762599.

The spelling of 21857439 in words is "twenty-one million, eight hundred fifty-seven thousand, four hundred thirty-nine".