18651865021 has 4 divisors (see below), whose sum is σ = 18652298812. Its totient is φ = 18651431232.

The previous prime is 18651865009. The next prime is 18651865039. The reversal of 18651865021 is 12056815681.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12056815681 = 2917 ⋅4133293.

It can be written as a sum of positive squares in 2 ways, for example, as 7636312996 + 11015552025 = 87386^2 + 104955^2 .

It is a cyclic number.

It is not a de Polignac number, because 18651865021 - 2⁷ = 18651864893 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18651865121) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 144300 + ... + 241093.

It is an arithmetic number, because the mean of its divisors is an integer number (4663074703).

Almost surely, 2^18651865021 is an apocalyptic number.

It is an amenable number.

18651865021 is a deficient number, since it is larger than the sum of its proper divisors (433791).

18651865021 is an equidigital number, since it uses as much as digits as its factorization.

18651865021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 433790.

The product of its (nonzero) digits is 115200, while the sum is 43.

The spelling of 18651865021 in words is "eighteen billion, six hundred fifty-one million, eight hundred sixty-five thousand, twenty-one".