18539117561 has 2 divisors, whose sum is σ = 18539117562. Its totient is φ = 18539117560.

The previous prime is 18539117533. The next prime is 18539117693. The reversal of 18539117561 is 16571193581.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18137355625 + 401761936 = 134675^2 + 20044^2 .

It is a cyclic number.

It is not a de Polignac number, because 18539117561 - 2²⁶ = 18472008697 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (18539117521) 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 as a sum of consecutive naturals, namely, 9269558780 + 9269558781.

It is an arithmetic number, because the mean of its divisors is an integer number (9269558781).

Almost surely, 2^18539117561 is an apocalyptic number.

It is an amenable number.

18539117561 is a deficient number, since it is larger than the sum of its proper divisors (1).

18539117561 is an equidigital number, since it uses as much as digits as its factorization.

18539117561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 226800, while the sum is 47.

The spelling of 18539117561 in words is "eighteen billion, five hundred thirty-nine million, one hundred seventeen thousand, five hundred sixty-one".