21897665 has 4 divisors (see below), whose sum is σ = 26277204. Its totient is φ = 17518128.

The previous prime is 21897661. The next prime is 21897703. The reversal of 21897665 is 56679812.

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 7579009 + 14318656 = 2753^2 + 3784^2 .

It is a cyclic number.

It is not a de Polignac number, because 21897665 - 2² = 21897661 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21897661) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2189762 + ... + 2189771.

It is an arithmetic number, because the mean of its divisors is an integer number (6569301).

Almost surely, 2^21897665 is an apocalyptic number.

It is an amenable number.

21897665 is a deficient number, since it is larger than the sum of its proper divisors (4379539).

21897665 is an equidigital number, since it uses as much as digits as its factorization.

21897665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4379538.

The product of its digits is 181440, while the sum is 44.

The square root of 21897665 is about 4679.4940965878. The cubic root of 21897665 is about 279.7687929793.

The spelling of 21897665 in words is "twenty-one million, eight hundred ninety-seven thousand, six hundred sixty-five".