21565613 has 4 divisors (see below), whose sum is σ = 21730368. Its totient is φ = 21400860.

The previous prime is 21565601. The next prime is 21565633. The reversal of 21565613 is 31656512.

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.

It is a cyclic number.

It is not a de Polignac number, because 21565613 - 2⁴ = 21565597 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 (21565633) 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, 82181 + ... + 82442.

It is an arithmetic number, because the mean of its divisors is an integer number (5432592).

Almost surely, 2^21565613 is an apocalyptic number.

It is an amenable number.

21565613 is a deficient number, since it is larger than the sum of its proper divisors (164755).

21565613 is a wasteful number, since it uses less digits than its factorization.

21565613 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 164754.

The product of its digits is 5400, while the sum is 29.

The square root of 21565613 is about 4643.8790897266. The cubic root of 21565613 is about 278.3474641931.

The spelling of 21565613 in words is "twenty-one million, five hundred sixty-five thousand, six hundred thirteen".