18556691821 has 2 divisors, whose sum is σ = 18556691822. Its totient is φ = 18556691820.

The previous prime is 18556691731. The next prime is 18556691837. The reversal of 18556691821 is 12819665581.

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., 14372413225 + 4184278596 = 119885^2 + 64686^2 .

It is a cyclic number.

It is not a de Polignac number, because 18556691821 - 2²⁹ = 18019820909 is a prime.

It is a super-2 number, since 2×18556691821² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18556691891) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9278345910 + 9278345911.

It is an arithmetic number, because the mean of its divisors is an integer number (9278345911).

Almost surely, 2^18556691821 is an apocalyptic number.

It is an amenable number.

18556691821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18556691821 is an equidigital number, since it uses as much as digits as its factorization.

18556691821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1036800, while the sum is 52.

The spelling of 18556691821 in words is "eighteen billion, five hundred fifty-six million, six hundred ninety-one thousand, eight hundred twenty-one".