21681211 has 2 divisors, whose sum is σ = 21681212. Its totient is φ = 21681210.

The previous prime is 21681193. The next prime is 21681217. The reversal of 21681211 is 11218612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21681211 - 2⁹ = 21680699 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21681217) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10840605 + 10840606.

It is an arithmetic number, because the mean of its divisors is an integer number (10840606).

Almost surely, 2^21681211 is an apocalyptic number.

21681211 is a deficient number, since it is larger than the sum of its proper divisors (1).

21681211 is an equidigital number, since it uses as much as digits as its factorization.

21681211 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 192, while the sum is 22.

The square root of 21681211 is about 4656.3087311732. The cubic root of 21681211 is about 278.8439195006.

Adding to 21681211 its reverse (11218612), we get a palindrome (32899823).

The spelling of 21681211 in words is "twenty-one million, six hundred eighty-one thousand, two hundred eleven".