21311111 has 2 divisors, whose sum is σ = 21311112. Its totient is φ = 21311110.

The previous prime is 21311107. The next prime is 21311113. The reversal of 21311111 is 11111312.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21311111 - 2² = 21311107 is a prime.

Together with 21311113, it forms a pair of twin primes.

It is a Chen prime.

21311111 is a modest number, since divided by 11111 gives 213 as remainder.

It is a junction number, because it is equal to n+sod(n) for n = 21311092 and 21311101.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21311113) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10655555 + 10655556.

It is an arithmetic number, because the mean of its divisors is an integer number (10655556).

Almost surely, 2^21311111 is an apocalyptic number.

21311111 is a deficient number, since it is larger than the sum of its proper divisors (1).

21311111 is an equidigital number, since it uses as much as digits as its factorization.

21311111 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6, while the sum is 11.

The square root of 21311111 is about 4616.3958885694. The cubic root of 21311111 is about 277.2481756245.

Adding to 21311111 its reverse (11111312), we get a palindrome (32422423).

The spelling of 21311111 in words is "twenty-one million, three hundred eleven thousand, one hundred eleven".