16661 has 2 divisors, whose sum is σ = 16662. Its totient is φ = 16660.

The previous prime is 16657. The next prime is 16673.

16661 is nontrivially palindromic in base 10.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14161 + 2500 = 119^2 + 50^2 .

It is a palprime.

It is a cyclic number.

It is not a de Polignac number, because 16661 - 2² = 16657 is a prime.

It is a Chen prime.

It is equal to p₁₉₂₈ and since 16661 and 1928 have the same sum of digits, it is a Honaker prime.

It is a plaindrome in base 11 and base 13.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 16661.

It is not a weakly prime, because it can be changed into another prime (16631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8330 + 8331.

It is an arithmetic number, because the mean of its divisors is an integer number (8331).

2¹⁶⁶⁶¹ is an apocalyptic number.

It is an amenable number.

16661 is a deficient number, since it is larger than the sum of its proper divisors (1).

16661 is an equidigital number, since it uses as much as digits as its factorization.

16661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 216, while the sum is 20.

The square root of 16661 is about 129.0774961021. The cubic root of 16661 is about 25.5407524716.

Subtracting from 16661 its sum of digits (20), we obtain a square (16641 = 129²).

The spelling of 16661 in words is "sixteen thousand, six hundred sixty-one".