21297439 has 4 divisors (see below), whose sum is σ = 21750624. Its totient is φ = 20844256.

The previous prime is 21297431. The next prime is 21297457. The reversal of 21297439 is 93479212.

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 21297439 - 2³ = 21297431 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21297398 and 21297407.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21297431) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 226522 + ... + 226615.

It is an arithmetic number, because the mean of its divisors is an integer number (5437656).

Almost surely, 2^21297439 is an apocalyptic number.

21297439 is a deficient number, since it is larger than the sum of its proper divisors (453185).

21297439 is an equidigital number, since it uses as much as digits as its factorization.

21297439 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 453184.

The product of its digits is 27216, while the sum is 37.

The square root of 21297439 is about 4614.9148421179. The cubic root of 21297439 is about 277.1888740401.

It can be divided in two parts, 21297 and 439, that added together give a triangular number (21736 = T₂₀₈).

The spelling of 21297439 in words is "twenty-one million, two hundred ninety-seven thousand, four hundred thirty-nine".