21687613 has 4 divisors (see below), whose sum is σ = 21696928. Its totient is φ = 21678300.

The previous prime is 21687599. The next prime is 21687619. The reversal of 21687613 is 31678612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21687613 - 2⁵ = 21687581 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21687619) 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, 2320 + ... + 6982.

It is an arithmetic number, because the mean of its divisors is an integer number (5424232).

Almost surely, 2^21687613 is an apocalyptic number.

It is an amenable number.

21687613 is a deficient number, since it is larger than the sum of its proper divisors (9315).

21687613 is an equidigital number, since it uses as much as digits as its factorization.

21687613 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9314.

The product of its digits is 12096, while the sum is 34.

The square root of 21687613 is about 4656.9961348492. The cubic root of 21687613 is about 278.8713623572.

Subtracting 21687613 from its reverse (31678612), we obtain a palindrome (9990999).

The spelling of 21687613 in words is "twenty-one million, six hundred eighty-seven thousand, six hundred thirteen".