21890191 has 4 divisors (see below), whose sum is σ = 21899592. Its totient is φ = 21880792.

The previous prime is 21890159. The next prime is 21890201. The reversal of 21890191 is 19109812.

It is a semiprime because it is the product of two primes, 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 21890191 - 2⁵ = 21890159 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21890111) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1680 + ... + 6826.

It is an arithmetic number, because the mean of its divisors is an integer number (5474898).

Almost surely, 2^21890191 is an apocalyptic number.

21890191 is a deficient number, since it is larger than the sum of its proper divisors (9401).

21890191 is an equidigital number, since it uses as much as digits as its factorization.

21890191 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9400.

The product of its (nonzero) digits is 1296, while the sum is 31.

The square root of 21890191 is about 4678.6954378331. The cubic root of 21890191 is about 279.7369596020.

It can be divided in two parts, 218 and 90191, that added together give a palindrome (90409).

The spelling of 21890191 in words is "twenty-one million, eight hundred ninety thousand, one hundred ninety-one".