21306811 has 2 divisors, whose sum is σ = 21306812. Its totient is φ = 21306810.

The previous prime is 21306749. The next prime is 21306823. The reversal of 21306811 is 11860312.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21306811 is a prime.

It is not a weakly prime, because it can be changed into another prime (21306881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10653405 + 10653406.

It is an arithmetic number, because the mean of its divisors is an integer number (10653406).

Almost surely, 2^21306811 is an apocalyptic number.

21306811 is a deficient number, since it is larger than the sum of its proper divisors (1).

21306811 is an equidigital number, since it uses as much as digits as its factorization.

21306811 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 21306811 is about 4615.9301337867. The cubic root of 21306811 is about 277.2295273343.

The spelling of 21306811 in words is "twenty-one million, three hundred six thousand, eight hundred eleven".