21316865 has 16 divisors (see below), whose sum is σ = 26247888. Its totient is φ = 16613376.

The previous prime is 21316859. The next prime is 21316891. The reversal of 21316865 is 56861312.

It is a happy number.

It can be written as a sum of positive squares in 8 ways, for example, as 9409 + 21307456 = 97^2 + 4616^2 .

It is a cyclic number.

It is not a de Polignac number, because 21316865 - 2⁴ = 21316849 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 67949 + ... + 68261.

It is an arithmetic number, because the mean of its divisors is an integer number (1640493).

Almost surely, 2^21316865 is an apocalyptic number.

It is an amenable number.

21316865 is a deficient number, since it is larger than the sum of its proper divisors (4931023).

21316865 is a wasteful number, since it uses less digits than its factorization.

21316865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 628.

The product of its digits is 8640, while the sum is 32.

The square root of 21316865 is about 4617.0190599563. The cubic root of 21316865 is about 277.2731257151.

The spelling of 21316865 in words is "twenty-one million, three hundred sixteen thousand, eight hundred sixty-five".