21889991 has 2 divisors, whose sum is σ = 21889992. Its totient is φ = 21889990.

The previous prime is 21889981. The next prime is 21889993. The reversal of 21889991 is 19998812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21889991 - 2⁶ = 21889927 is a prime.

Together with 21889993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21889993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10944995 + 10944996.

It is an arithmetic number, because the mean of its divisors is an integer number (10944996).

Almost surely, 2^21889991 is an apocalyptic number.

21889991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21889991 is an equidigital number, since it uses as much as digits as its factorization.

21889991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 93312, while the sum is 47.

The square root of 21889991 is about 4678.6740643050. The cubic root of 21889991 is about 279.7361076593.

It can be divided in two parts, 218 and 89991, that added together give a palindrome (90209).

The spelling of 21889991 in words is "twenty-one million, eight hundred eighty-nine thousand, nine hundred ninety-one".