21539929 has 4 divisors (see below), whose sum is σ = 21677284. Its totient is φ = 21402576.

The previous prime is 21539899. The next prime is 21539933. The reversal of 21539929 is 92993512.

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

It can be written as a sum of positive squares in 2 ways, for example, as 10497600 + 11042329 = 3240^2 + 3323^2 .

It is a cyclic number.

It is not a de Polignac number, because 21539929 - 2⁹ = 21539417 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21539891 and 21539900.

It is not an unprimeable number, because it can be changed into a prime (21539029) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 68442 + ... + 68755.

It is an arithmetic number, because the mean of its divisors is an integer number (5419321).

Almost surely, 2^21539929 is an apocalyptic number.

It is an amenable number.

21539929 is a deficient number, since it is larger than the sum of its proper divisors (137355).

21539929 is a wasteful number, since it uses less digits than its factorization.

21539929 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 137354.

The product of its digits is 43740, while the sum is 40.

The square root of 21539929 is about 4641.1129053278. The cubic root of 21539929 is about 278.2369191282.

The spelling of 21539929 in words is "twenty-one million, five hundred thirty-nine thousand, nine hundred twenty-nine".