21705139 has 2 divisors, whose sum is σ = 21705140. Its totient is φ = 21705138.

The previous prime is 21705133. The next prime is 21705149. The reversal of 21705139 is 93150712.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21705139 is a prime.

It is a super-2 number, since 2×21705139² = 942226118018642, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21705133) 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, 10852569 + 10852570.

It is an arithmetic number, because the mean of its divisors is an integer number (10852570).

Almost surely, 2^21705139 is an apocalyptic number.

21705139 is a deficient number, since it is larger than the sum of its proper divisors (1).

21705139 is an equidigital number, since it uses as much as digits as its factorization.

21705139 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1890, while the sum is 28.

The square root of 21705139 is about 4658.8774398990. The cubic root of 21705139 is about 278.9464618090.

The spelling of 21705139 in words is "twenty-one million, seven hundred five thousand, one hundred thirty-nine".