21011111 has 4 divisors (see below), whose sum is σ = 22921224. Its totient is φ = 19101000.

The previous prime is 21011083. The next prime is 21011141. The reversal of 21011111 is 11111012.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21011111 is a prime.

It is a Duffinian number.

21011111 is a modest number, since divided by 11111 gives 210 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21011141) 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, 955040 + ... + 955061.

It is an arithmetic number, because the mean of its divisors is an integer number (5730306).

Almost surely, 2^21011111 is an apocalyptic number.

21011111 is a deficient number, since it is larger than the sum of its proper divisors (1910113).

21011111 is a wasteful number, since it uses less digits than its factorization.

21011111 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1910112.

The product of its (nonzero) digits is 2, while the sum is 8.

The square root of 21011111 is about 4583.7878441307. The cubic root of 21011111 is about 275.9410668472.

Adding to 21011111 its reverse (11111012), we get a palindrome (32122123).

Subtracting from 21011111 its reverse (11111012), we obtain a palindrome (9900099).

The spelling of 21011111 in words is "twenty-one million, eleven thousand, one hundred eleven".