21778181 has 2 divisors, whose sum is σ = 21778182. Its totient is φ = 21778180.

The previous prime is 21778157. The next prime is 21778187. The reversal of 21778181 is 18187712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20557156 + 1221025 = 4534^2 + 1105^2 .

It is a cyclic number.

It is not a de Polignac number, because 21778181 - 2⁶ = 21778117 is a prime.

It is a super-2 number, since 2×21778181² = 948578335337522, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21778187) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10889090 + 10889091.

It is an arithmetic number, because the mean of its divisors is an integer number (10889091).

Almost surely, 2^21778181 is an apocalyptic number.

It is an amenable number.

21778181 is a deficient number, since it is larger than the sum of its proper divisors (1).

21778181 is an equidigital number, since it uses as much as digits as its factorization.

21778181 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6272, while the sum is 35.

The square root of 21778181 is about 4666.7098688476. The cubic root of 21778181 is about 279.2590144421.

The spelling of 21778181 in words is "twenty-one million, seven hundred seventy-eight thousand, one hundred eighty-one".