21565371 has 4 divisors (see below), whose sum is σ = 28753832. Its totient is φ = 14376912.

The previous prime is 21565337. The next prime is 21565409. The reversal of 21565371 is 17356512.

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

It is not a de Polignac number, because 21565371 - 2¹⁵ = 21532603 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21565471) 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, 3594226 + ... + 3594231.

It is an arithmetic number, because the mean of its divisors is an integer number (7188458).

Almost surely, 2^21565371 is an apocalyptic number.

21565371 is a deficient number, since it is larger than the sum of its proper divisors (7188461).

21565371 is an equidigital number, since it uses as much as digits as its factorization.

21565371 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7188460.

The product of its digits is 6300, while the sum is 30.

The square root of 21565371 is about 4643.8530338502. The cubic root of 21565371 is about 278.3464230241.

The spelling of 21565371 in words is "twenty-one million, five hundred sixty-five thousand, three hundred seventy-one".