21768865 has 4 divisors (see below), whose sum is σ = 26122644. Its totient is φ = 17415088.

The previous prime is 21768853. The next prime is 21768883. The reversal of 21768865 is 56886712.

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 16353936 + 5414929 = 4044^2 + 2327^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21768865 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, 2176882 + ... + 2176891.

It is an arithmetic number, because the mean of its divisors is an integer number (6530661).

Almost surely, 2^21768865 is an apocalyptic number.

It is an amenable number.

21768865 is a deficient number, since it is larger than the sum of its proper divisors (4353779).

21768865 is an equidigital number, since it uses as much as digits as its factorization.

21768865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4353778.

The product of its digits is 161280, while the sum is 43.

The square root of 21768865 is about 4665.7116284657. The cubic root of 21768865 is about 279.2191894444.

The spelling of 21768865 in words is "twenty-one million, seven hundred sixty-eight thousand, eight hundred sixty-five".