21768389 has 4 divisors (see below), whose sum is σ = 21778080. Its totient is φ = 21758700.

The previous prime is 21768361. The next prime is 21768391. The reversal of 21768389 is 98386712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21768389 - 2⁸ = 21768133 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21768349) 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, 464 + ... + 6614.

It is an arithmetic number, because the mean of its divisors is an integer number (5444520).

Almost surely, 2^21768389 is an apocalyptic number.

It is an amenable number.

21768389 is a deficient number, since it is larger than the sum of its proper divisors (9691).

21768389 is an equidigital number, since it uses as much as digits as its factorization.

21768389 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9690.

The product of its digits is 145152, while the sum is 44.

The square root of 21768389 is about 4665.6606177475. The cubic root of 21768389 is about 279.2171542855.

The spelling of 21768389 in words is "twenty-one million, seven hundred sixty-eight thousand, three hundred eighty-nine".