21565081 has 4 divisors (see below), whose sum is σ = 21586432. Its totient is φ = 21543732.

The previous prime is 21565079. The next prime is 21565087. The reversal of 21565081 is 18056512.

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 21565081 - 2¹ = 21565079 is a prime.

It is a super-2 number, since 2×21565081² = 930105437073122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21565087) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9081 + ... + 11206.

It is an arithmetic number, because the mean of its divisors is an integer number (5396608).

Almost surely, 2^21565081 is an apocalyptic number.

It is an amenable number.

21565081 is a deficient number, since it is larger than the sum of its proper divisors (21351).

21565081 is a wasteful number, since it uses less digits than its factorization.

21565081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21350.

The product of its (nonzero) digits is 2400, while the sum is 28.

The square root of 21565081 is about 4643.8218096736. The cubic root of 21565081 is about 278.3451753321.

The spelling of 21565081 in words is "twenty-one million, five hundred sixty-five thousand, eighty-one".