21778189 has 2 divisors, whose sum is σ = 21778190. Its totient is φ = 21778188.

The previous prime is 21778187. The next prime is 21778193. The reversal of 21778189 is 98187712.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21696964 + 81225 = 4658^2 + 285^2 .

It is a cyclic number.

It is not a de Polignac number, because 21778189 - 2¹ = 21778187 is a prime.

It is a super-2 number, since 2×21778189² = 948579032239442, which contains 22 as substring.

Together with 21778187, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21778181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10889094 + 10889095.

It is an arithmetic number, because the mean of its divisors is an integer number (10889095).

Almost surely, 2^21778189 is an apocalyptic number.

It is an amenable number.

21778189 is a deficient number, since it is larger than the sum of its proper divisors (1).

21778189 is an equidigital number, since it uses as much as digits as its factorization.

21778189 is an evil number, because the sum of its binary digits is even.

The product of its digits is 56448, while the sum is 43.

The square root of 21778189 is about 4666.7107259825. The cubic root of 21778189 is about 279.2590486365.

The spelling of 21778189 in words is "twenty-one million, seven hundred seventy-eight thousand, one hundred eighty-nine".