18191021213 has 4 divisors (see below), whose sum is σ = 18199567740. Its totient is φ = 18182474688.

The previous prime is 18191021209. The next prime is 18191021263. The reversal of 18191021213 is 31212019181.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 31212019181 = 7 ⋅4458859883.

It can be written as a sum of positive squares in 2 ways, for example, as 8724120409 + 9466900804 = 93403^2 + 97298^2 .

It is a cyclic number.

It is not a de Polignac number, because 18191021213 - 2² = 18191021209 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18191021263) 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, 4270070 + ... + 4274327.

It is an arithmetic number, because the mean of its divisors is an integer number (4549891935).

Almost surely, 2^18191021213 is an apocalyptic number.

It is an amenable number.

18191021213 is a deficient number, since it is larger than the sum of its proper divisors (8546527).

18191021213 is an equidigital number, since it uses as much as digits as its factorization.

18191021213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8546526.

The product of its (nonzero) digits is 864, while the sum is 29.

The spelling of 18191021213 in words is "eighteen billion, one hundred ninety-one million, twenty-one thousand, two hundred thirteen".