18531521821 has 2 divisors, whose sum is σ = 18531521822. Its totient is φ = 18531521820.

The previous prime is 18531521791. The next prime is 18531521831. The reversal of 18531521821 is 12812513581.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10239416100 + 8292105721 = 101190^2 + 91061^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18531521821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18531521831) 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, 9265760910 + 9265760911.

It is an arithmetic number, because the mean of its divisors is an integer number (9265760911).

Almost surely, 2^18531521821 is an apocalyptic number.

It is an amenable number.

18531521821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18531521821 is an equidigital number, since it uses as much as digits as its factorization.

18531521821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 19200, while the sum is 37.

The spelling of 18531521821 in words is "eighteen billion, five hundred thirty-one million, five hundred twenty-one thousand, eight hundred twenty-one".