21018889 has 4 divisors (see below), whose sum is σ = 21086356. Its totient is φ = 20951424.

The previous prime is 21018869. The next prime is 21018929. The reversal of 21018889 is 98881012.

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 1729225 + 19289664 = 1315^2 + 4392^2 .

It is a cyclic number.

It is not a de Polignac number, because 21018889 - 2⁵ = 21018857 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21018839) 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, 33264 + ... + 33889.

It is an arithmetic number, because the mean of its divisors is an integer number (5271589).

Almost surely, 2^21018889 is an apocalyptic number.

It is an amenable number.

21018889 is a deficient number, since it is larger than the sum of its proper divisors (67467).

21018889 is an equidigital number, since it uses as much as digits as its factorization.

21018889 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67466.

The product of its (nonzero) digits is 9216, while the sum is 37.

The square root of 21018889 is about 4584.6361905826. The cubic root of 21018889 is about 275.9751124027.

The spelling of 21018889 in words is "twenty-one million, eighteen thousand, eight hundred eighty-nine".