21163865 has 8 divisors (see below), whose sum is σ = 25937280. Its totient is φ = 16570672.

The previous prime is 21163859. The next prime is 21163867. The reversal of 21163865 is 56836112.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21163865 - 2²⁴ = 4386649 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21163867) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44795 + ... + 45264.

It is an arithmetic number, because the mean of its divisors is an integer number (3242160).

Almost surely, 2^21163865 is an apocalyptic number.

It is an amenable number.

21163865 is a deficient number, since it is larger than the sum of its proper divisors (4773415).

21163865 is an equidigital number, since it uses as much as digits as its factorization.

21163865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 90111.

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

The square root of 21163865 is about 4600.4200895136. The cubic root of 21163865 is about 276.6081641112.

Adding to 21163865 its reverse (56836112), we get a palindrome (77999977).

The spelling of 21163865 in words is "twenty-one million, one hundred sixty-three thousand, eight hundred sixty-five".