18981821 has 2 divisors, whose sum is σ = 18981822. Its totient is φ = 18981820.

The previous prime is 18981773. The next prime is 18981841. The reversal of 18981821 is 12818981.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12880921 + 6100900 = 3589^2 + 2470^2 .

It is a cyclic number.

It is not a de Polignac number, because 18981821 - 2²² = 14787517 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18981841) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9490910 + 9490911.

It is an arithmetic number, because the mean of its divisors is an integer number (9490911).

Almost surely, 2^18981821 is an apocalyptic number.

It is an amenable number.

18981821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18981821 is an equidigital number, since it uses as much as digits as its factorization.

18981821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9216, while the sum is 38.

The square root of 18981821 is about 4356.8131701968. The cubic root of 18981821 is about 266.7550344288.

The spelling of 18981821 in words is "eighteen million, nine hundred eighty-one thousand, eight hundred twenty-one".