21905239 has 2 divisors, whose sum is σ = 21905240. Its totient is φ = 21905238.

The previous prime is 21905227. The next prime is 21905263. The reversal of 21905239 is 93250912.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21905239 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21905239.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21905209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10952619 + 10952620.

It is an arithmetic number, because the mean of its divisors is an integer number (10952620).

Almost surely, 2^21905239 is an apocalyptic number.

21905239 is a deficient number, since it is larger than the sum of its proper divisors (1).

21905239 is an equidigital number, since it uses as much as digits as its factorization.

21905239 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4860, while the sum is 31.

The square root of 21905239 is about 4680.3033021376. The cubic root of 21905239 is about 279.8010448896.

The spelling of 21905239 in words is "twenty-one million, nine hundred five thousand, two hundred thirty-nine".