21129239 has 2 divisors, whose sum is σ = 21129240. Its totient is φ = 21129238.

The previous prime is 21129221. The next prime is 21129263. The reversal of 21129239 is 93292112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21129239 - 2¹⁶ = 21063703 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21129209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10564619 + 10564620.

It is an arithmetic number, because the mean of its divisors is an integer number (10564620).

Almost surely, 2^21129239 is an apocalyptic number.

21129239 is a deficient number, since it is larger than the sum of its proper divisors (1).

21129239 is an equidigital number, since it uses as much as digits as its factorization.

21129239 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1944, while the sum is 29.

The square root of 21129239 is about 4596.6551969883. The cubic root of 21129239 is about 276.4572297640.

The spelling of 21129239 in words is "twenty-one million, one hundred twenty-nine thousand, two hundred thirty-nine".