21078865 has 4 divisors (see below), whose sum is σ = 25294644. Its totient is φ = 16863088.

The previous prime is 21078857. The next prime is 21078877. The reversal of 21078865 is 56887012.

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

It can be written as a sum of positive squares in 2 ways, for example, as 11048976 + 10029889 = 3324^2 + 3167^2 .

It is a cyclic number.

It is not a de Polignac number, because 21078865 - 2³ = 21078857 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2107882 + ... + 2107891.

It is an arithmetic number, because the mean of its divisors is an integer number (6323661).

Almost surely, 2^21078865 is an apocalyptic number.

It is an amenable number.

21078865 is a deficient number, since it is larger than the sum of its proper divisors (4215779).

21078865 is an equidigital number, since it uses as much as digits as its factorization.

21078865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4215778.

The product of its (nonzero) digits is 26880, while the sum is 37.

The square root of 21078865 is about 4591.1725081944. The cubic root of 21078865 is about 276.2373553312.

The spelling of 21078865 in words is "twenty-one million, seventy-eight thousand, eight hundred sixty-five".