21405139 has 4 divisors (see below), whose sum is σ = 24463024. Its totient is φ = 18347256.

The previous prime is 21405127. The next prime is 21405149. The reversal of 21405139 is 93150412.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21405139 - 2¹⁷ = 21274067 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21405149) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1528932 + ... + 1528945.

It is an arithmetic number, because the mean of its divisors is an integer number (6115756).

Almost surely, 2^21405139 is an apocalyptic number.

21405139 is a deficient number, since it is larger than the sum of its proper divisors (3057885).

21405139 is an equidigital number, since it uses as much as digits as its factorization.

21405139 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3057884.

The product of its (nonzero) digits is 1080, while the sum is 25.

The square root of 21405139 is about 4626.5688150075. The cubic root of 21405139 is about 277.6553316982.

The spelling of 21405139 in words is "twenty-one million, four hundred five thousand, one hundred thirty-nine".