18691810021 has 4 divisors (see below), whose sum is σ = 18694374700. Its totient is φ = 18689245344.

The previous prime is 18691810019. The next prime is 18691810043. The reversal of 18691810021 is 12001819681.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10050062500 + 8641747521 = 100250^2 + 92961^2 .

It is a cyclic number.

It is not a de Polignac number, because 18691810021 - 2¹ = 18691810019 is a prime.

It is a super-2 number, since 2×18691810021² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18691810061) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1271376 + ... + 1285993.

It is an arithmetic number, because the mean of its divisors is an integer number (4673593675).

Almost surely, 2^18691810021 is an apocalyptic number.

It is an amenable number.

18691810021 is a deficient number, since it is larger than the sum of its proper divisors (2564679).

18691810021 is an equidigital number, since it uses as much as digits as its factorization.

18691810021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2564678.

The product of its (nonzero) digits is 6912, while the sum is 37.

The spelling of 18691810021 in words is "eighteen billion, six hundred ninety-one million, eight hundred ten thousand, twenty-one".