18116561 has 4 divisors (see below), whose sum is σ = 18741300. Its totient is φ = 17491824.

The previous prime is 18116537. The next prime is 18116587. The reversal of 18116561 is 16561181.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9265936 + 8850625 = 3044^2 + 2975^2 .

It is a cyclic number.

It is not a de Polignac number, because 18116561 - 2¹⁴ = 18100177 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29), and also a Moran number because the ratio is a prime number: 624709 = 18116561 / (1 + 8 + 1 + 1 + 6 + 5 + 6 + 1).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18116521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 312326 + ... + 312383.

It is an arithmetic number, because the mean of its divisors is an integer number (4685325).

Almost surely, 2^18116561 is an apocalyptic number.

18116561 is the 1904-th centered decagonal number.

It is an amenable number.

18116561 is a deficient number, since it is larger than the sum of its proper divisors (624739).

18116561 is an equidigital number, since it uses as much as digits as its factorization.

18116561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 624738.

The product of its digits is 1440, while the sum is 29.

The square root of 18116561 is about 4256.3553658030. The cubic root of 18116561 is about 262.6386194539.

The spelling of 18116561 in words is "eighteen million, one hundred sixteen thousand, five hundred sixty-one".