16561 has 2 divisors, whose sum is σ = 16562. Its totient is φ = 16560.

The previous prime is 16553. The next prime is 16567.

16561 = 9⁴ + 10⁴.

16561 is nontrivially palindromic in base 7 and base 10.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10000 + 6561 = 100^2 + 81^2 .

It is a palprime.

It is a cyclic number.

It is not a de Polignac number, because 16561 - 2³ = 16553 is a prime.

It is a Chen prime.

It is an alternating number because its digits alternate between odd and even.

It is not a weakly prime, because it can be changed into another prime (16567) 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, 8280 + 8281.

It is an arithmetic number, because the mean of its divisors is an integer number (8281).

2¹⁶⁵⁶¹ is an apocalyptic number.

It is an amenable number.

16561 is a deficient number, since it is larger than the sum of its proper divisors (1).

16561 is an equidigital number, since it uses as much as digits as its factorization.

16561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 180, while the sum is 19.

The square root of 16561 is about 128.6895489152. The cubic root of 16561 is about 25.4895510182.

The spelling of 16561 in words is "sixteen thousand, five hundred sixty-one".