18857537821 has 4 divisors (see below), whose sum is σ = 18877837500. Its totient is φ = 18837238144.

The previous prime is 18857537807. The next prime is 18857537939. The reversal of 18857537821 is 12873575881.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12873575881 = 17117 ⋅752093.

It can be written as a sum of positive squares in 2 ways, for example, as 3774259225 + 15083278596 = 61435^2 + 122814^2 .

It is a cyclic number.

It is not a de Polignac number, because 18857537821 - 2⁷ = 18857537693 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 (18857531821) 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, 10148446 + ... + 10150303.

It is an arithmetic number, because the mean of its divisors is an integer number (4719459375).

Almost surely, 2^18857537821 is an apocalyptic number.

It is an amenable number.

18857537821 is a deficient number, since it is larger than the sum of its proper divisors (20299679).

18857537821 is an equidigital number, since it uses as much as digits as its factorization.

18857537821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20299678.

The product of its digits is 3763200, while the sum is 55.

The spelling of 18857537821 in words is "eighteen billion, eight hundred fifty-seven million, five hundred thirty-seven thousand, eight hundred twenty-one".