21129439 has 2 divisors, whose sum is σ = 21129440. Its totient is φ = 21129438.

The previous prime is 21129403. The next prime is 21129467. The reversal of 21129439 is 93492112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21129439 - 2¹¹ = 21127391 is a prime.

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 21129439.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21129499) 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 as a sum of consecutive naturals, namely, 10564719 + 10564720.

It is an arithmetic number, because the mean of its divisors is an integer number (10564720).

Almost surely, 2^21129439 is an apocalyptic number.

21129439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21129439 is an equidigital number, since it uses as much as digits as its factorization.

21129439 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3888, while the sum is 31.

The square root of 21129439 is about 4596.6769518860. The cubic root of 21129439 is about 276.4581020351.

The spelling of 21129439 in words is "twenty-one million, one hundred twenty-nine thousand, four hundred thirty-nine".