18208561 has 8 divisors (see below), whose sum is σ = 21151424. Its totient is φ = 15351120.

The previous prime is 18208543. The next prime is 18208573. The reversal of 18208561 is 16580281.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 18208561 - 2¹⁹ = 17684273 is a prime.

It is not an unprimeable number, because it can be changed into a prime (18208591) 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 7 ways as a sum of consecutive naturals, for example, 20895 + ... + 21748.

It is an arithmetic number, because the mean of its divisors is an integer number (2643928).

Almost surely, 2^18208561 is an apocalyptic number.

It is an amenable number.

18208561 is a deficient number, since it is larger than the sum of its proper divisors (2942863).

18208561 is an equidigital number, since it uses as much as digits as its factorization.

18208561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42711.

The product of its (nonzero) digits is 3840, while the sum is 31.

The square root of 18208561 is about 4267.1490482522. The cubic root of 18208561 is about 263.0824484765.

It can be divided in two parts, 18208 and 561, that added together give a square (18769 = 137²).

The spelling of 18208561 in words is "eighteen million, two hundred eight thousand, five hundred sixty-one".