18685636561 has 4 divisors (see below), whose sum is σ = 18686044224. Its totient is φ = 18685228900.

The previous prime is 18685636537. The next prime is 18685636573. The reversal of 18685636561 is 16563658681.

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: 16563658681 = 14627 ⋅1132403.

It is a cyclic number.

It is not a de Polignac number, because 18685636561 - 2⁹ = 18685636049 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18685636591) 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, 124885 + ... + 230146.

It is an arithmetic number, because the mean of its divisors is an integer number (4671511056).

Almost surely, 2^18685636561 is an apocalyptic number.

It is an amenable number.

18685636561 is a deficient number, since it is larger than the sum of its proper divisors (407663).

18685636561 is an equidigital number, since it uses as much as digits as its factorization.

18685636561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 407662.

The product of its digits is 6220800, while the sum is 55.

The spelling of 18685636561 in words is "eighteen billion, six hundred eighty-five million, six hundred thirty-six thousand, five hundred sixty-one".