18666561 has 16 divisors (see below), whose sum is σ = 26440128. Its totient is φ = 11673600.

The previous prime is 18666541. The next prime is 18666563. The reversal of 18666561 is 16566681.

It is not a de Polignac number, because 18666561 - 2⁶ = 18666497 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (18666563) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28801 + ... + 29441.

It is an arithmetic number, because the mean of its divisors is an integer number (1652508).

Almost surely, 2^18666561 is an apocalyptic number.

It is an amenable number.

18666561 is a deficient number, since it is larger than the sum of its proper divisors (7773567).

18666561 is a wasteful number, since it uses less digits than its factorization.

18666561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1232.

The product of its digits is 51840, while the sum is 39.

The square root of 18666561 is about 4320.4815703808. The cubic root of 18666561 is about 265.2699799853.

The spelling of 18666561 in words is "eighteen million, six hundred sixty-six thousand, five hundred sixty-one".