18221821 has 2 divisors, whose sum is σ = 18221822. Its totient is φ = 18221820.

The previous prime is 18221783. The next prime is 18221837. The reversal of 18221821 is 12812281.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12996025 + 5225796 = 3605^2 + 2286^2 .

It is a cyclic number.

It is not a de Polignac number, because 18221821 - 2¹⁷ = 18090749 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18221851) 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, 9110910 + 9110911.

It is an arithmetic number, because the mean of its divisors is an integer number (9110911).

Almost surely, 2^18221821 is an apocalyptic number.

It is an amenable number.

18221821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18221821 is an equidigital number, since it uses as much as digits as its factorization.

18221821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 512, while the sum is 25.

The square root of 18221821 is about 4268.7024960754. The cubic root of 18221821 is about 263.1462943932.

The spelling of 18221821 in words is "eighteen million, two hundred twenty-one thousand, eight hundred twenty-one".