21012239 has 2 divisors, whose sum is σ = 21012240. Its totient is φ = 21012238.

The previous prime is 21012227. The next prime is 21012241. The reversal of 21012239 is 93221012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21012239 - 2²⁰ = 19963663 is a prime.

Together with 21012241, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21012239.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21012259) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10506119 + 10506120.

It is an arithmetic number, because the mean of its divisors is an integer number (10506120).

Almost surely, 2^21012239 is an apocalyptic number.

21012239 is a deficient number, since it is larger than the sum of its proper divisors (1).

21012239 is an equidigital number, since it uses as much as digits as its factorization.

21012239 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 216, while the sum is 20.

The square root of 21012239 is about 4583.9108848231. The cubic root of 21012239 is about 275.9460048053.

The spelling of 21012239 in words is "twenty-one million, twelve thousand, two hundred thirty-nine".