18521510921 has 4 divisors (see below), whose sum is σ = 18782377344. Its totient is φ = 18260644500.

The previous prime is 18521510911. The next prime is 18521510927. The reversal of 18521510921 is 12901512581.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12901512581 = 9791 ⋅1317691.

It is a cyclic number.

It is not a de Polignac number, because 18521510921 - 2¹⁸ = 18521248777 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (18521510927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 130433105 + ... + 130433246.

It is an arithmetic number, because the mean of its divisors is an integer number (4695594336).

Almost surely, 2^18521510921 is an apocalyptic number.

It is an amenable number.

18521510921 is a deficient number, since it is larger than the sum of its proper divisors (260866423).

18521510921 is an equidigital number, since it uses as much as digits as its factorization.

18521510921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 260866422.

The product of its (nonzero) digits is 7200, while the sum is 35.

The spelling of 18521510921 in words is "eighteen billion, five hundred twenty-one million, five hundred ten thousand, nine hundred twenty-one".