21209239 has 8 divisors (see below), whose sum is σ = 22159872. Its totient is φ = 20275320.

The previous prime is 21209231. The next prime is 21209311. The reversal of 21209239 is 93290212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21209239 - 2³ = 21209231 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21209231) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1549 + ... + 6694.

It is an arithmetic number, because the mean of its divisors is an integer number (2769984).

Almost surely, 2^21209239 is an apocalyptic number.

21209239 is a deficient number, since it is larger than the sum of its proper divisors (950633).

21209239 is an equidigital number, since it uses as much as digits as its factorization.

21209239 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8357.

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 21209239 is about 4605.3489552910. The cubic root of 21209239 is about 276.8056998656.

The spelling of 21209239 in words is "twenty-one million, two hundred nine thousand, two hundred thirty-nine".