21778111 has 2 divisors, whose sum is σ = 21778112. Its totient is φ = 21778110.

The previous prime is 21778109. The next prime is 21778117. The reversal of 21778111 is 11187712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21778111 - 2¹ = 21778109 is a prime.

It is a super-2 number, since 2×21778111² = 948572237456642, which contains 22 as substring.

Together with 21778109, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21778111.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21778117) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10889055 + 10889056.

It is an arithmetic number, because the mean of its divisors is an integer number (10889056).

Almost surely, 2^21778111 is an apocalyptic number.

21778111 is a deficient number, since it is larger than the sum of its proper divisors (1).

21778111 is an equidigital number, since it uses as much as digits as its factorization.

21778111 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 784, while the sum is 28.

The square root of 21778111 is about 4666.7023689110. The cubic root of 21778111 is about 279.2587152412.

The spelling of 21778111 in words is "twenty-one million, seven hundred seventy-eight thousand, one hundred eleven".