18661 has 2 divisors, whose sum is σ = 18662. Its totient is φ = 18660.

The previous prime is 18637. The next prime is 18671. The reversal of 18661 is 16681.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12100 + 6561 = 110^2 + 81^2 .

It is a cyclic number.

It is not a de Polignac number, because 18661 - 2⁹ = 18149 is a prime.

It is a Chen prime.

18661 is a lucky number.

It is a nialpdrome in base 6 and base 12.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18671) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9330 + 9331.

It is an arithmetic number, because the mean of its divisors is an integer number (9331).

2¹⁸⁶⁶¹ is an apocalyptic number.

It is an amenable number.

18661 is a deficient number, since it is larger than the sum of its proper divisors (1).

18661 is an equidigital number, since it uses as much as digits as its factorization.

18661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 288, while the sum is 22.

The square root of 18661 is about 136.6052707621. The cubic root of 18661 is about 26.5243634963.

The spelling of 18661 in words is "eighteen thousand, six hundred sixty-one".