21005323 has 4 divisors (see below), whose sum is σ = 21020920. Its totient is φ = 20989728.

The previous prime is 21005311. The next prime is 21005329. The reversal of 21005323 is 32350012.

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 21005323 - 2⁵ = 21005291 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21005297 and 21005306.

It is not an unprimeable number, because it can be changed into a prime (21005329) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5565 + ... + 8542.

It is an arithmetic number, because the mean of its divisors is an integer number (5255230).

Almost surely, 2^21005323 is an apocalyptic number.

21005323 is a deficient number, since it is larger than the sum of its proper divisors (15597).

21005323 is a wasteful number, since it uses less digits than its factorization.

21005323 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15596.

The product of its (nonzero) digits is 180, while the sum is 16.

The square root of 21005323 is about 4583.1564450715. The cubic root of 21005323 is about 275.9157263885.

Adding to 21005323 its reverse (32350012), we get a palindrome (53355335).

The spelling of 21005323 in words is "twenty-one million, five thousand, three hundred twenty-three".