21281111 has 2 divisors, whose sum is σ = 21281112. Its totient is φ = 21281110.

The previous prime is 21281107. The next prime is 21281137. The reversal of 21281111 is 11118212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21281111 - 2² = 21281107 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21281111.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21281101) 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, 10640555 + 10640556.

It is an arithmetic number, because the mean of its divisors is an integer number (10640556).

Almost surely, 2^21281111 is an apocalyptic number.

21281111 is a deficient number, since it is larger than the sum of its proper divisors (1).

21281111 is an equidigital number, since it uses as much as digits as its factorization.

21281111 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 32, while the sum is 17.

The square root of 21281111 is about 4613.1454561936. The cubic root of 21281111 is about 277.1180189316.

Adding to 21281111 its reverse (11118212), we get a palindrome (32399323).

The spelling of 21281111 in words is "twenty-one million, two hundred eighty-one thousand, one hundred eleven".