21705613 has 4 divisors (see below), whose sum is σ = 21717180. Its totient is φ = 21694048.

The previous prime is 21705589. The next prime is 21705631. The reversal of 21705613 is 31650712.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 3617604 + 18088009 = 1902^2 + 4253^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21705613 is a prime.

It is a super-2 number, since 2×21705613² = 942267271411538, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21709613) 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 in 3 ways as a sum of consecutive naturals, for example, 2248 + ... + 6961.

It is an arithmetic number, because the mean of its divisors is an integer number (5429295).

Almost surely, 2^21705613 is an apocalyptic number.

It is an amenable number.

21705613 is a deficient number, since it is larger than the sum of its proper divisors (11567).

21705613 is an equidigital number, since it uses as much as digits as its factorization.

21705613 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11566.

The product of its (nonzero) digits is 1260, while the sum is 25.

The square root of 21705613 is about 4658.9283102447. The cubic root of 21705613 is about 278.9484923521.

The spelling of 21705613 in words is "twenty-one million, seven hundred five thousand, six hundred thirteen".