21020111111 has 2 divisors, whose sum is σ = 21020111112. Its totient is φ = 21020111110.

The previous prime is 21020111087. The next prime is 21020111153. The reversal of 21020111111 is 11111102012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21020111111 - 2¹⁰ = 21020110087 is a prime.

It is a super-2 number, since 2×21020111111² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

21020111111 is a modest number, since divided by 111111 gives 21020 as remainder.

It is a junction number, because it is equal to n+sod(n) for n = 21020111092 and 21020111101.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21020111611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510055555 + 10510055556.

It is an arithmetic number, because the mean of its divisors is an integer number (10510055556).

Almost surely, 2^21020111111 is an apocalyptic number.

21020111111 is a deficient number, since it is larger than the sum of its proper divisors (1).

21020111111 is an equidigital number, since it uses as much as digits as its factorization.

21020111111 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4, while the sum is 11.

Adding to 21020111111 its reverse (11111102012), we get a palindrome (32131213123).

Subtracting from 21020111111 its reverse (11111102012), we obtain a palindrome (9909009099).

The spelling of 21020111111 in words is "twenty-one billion, twenty million, one hundred eleven thousand, one hundred eleven".