21105811 has 2 divisors, whose sum is σ = 21105812. Its totient is φ = 21105810.

The previous prime is 21105781. The next prime is 21105863. The reversal of 21105811 is 11850112.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21105811 - 2⁷ = 21105683 is a prime.

It is equal to p_1336240 and since 21105811 and 1336240 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21105911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10552905 + 10552906.

It is an arithmetic number, because the mean of its divisors is an integer number (10552906).

Almost surely, 2^21105811 is an apocalyptic number.

21105811 is a deficient number, since it is larger than the sum of its proper divisors (1).

21105811 is an equidigital number, since it uses as much as digits as its factorization.

21105811 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 80, while the sum is 19.

The square root of 21105811 is about 4594.1061154484. The cubic root of 21105811 is about 276.3550138208.

Adding to 21105811 its reverse (11850112), we get a palindrome (32955923).

It can be divided in two parts, 2110 and 5811, that added together give a square (7921 = 89²).

The spelling of 21105811 in words is "twenty-one million, one hundred five thousand, eight hundred eleven".