561666 has 32 divisors (see below), whose sum is σ = 1317888. Its totient is φ = 156240.

The previous prime is 561607. The next prime is 561667. The reversal of 561666 is 666165.

561666 is nontrivially palindromic in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (561667) by changing a digit.

561666 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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 in 15 ways as a sum of consecutive naturals, for example, 1651 + ... + 1961.

It is an arithmetic number, because the mean of its divisors is an integer number (41184).

2⁵⁶¹⁶⁶⁶ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 561666, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (658944).

561666 is an abundant number, since it is smaller than the sum of its proper divisors (756222).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

561666 is a wasteful number, since it uses less digits than its factorization.

561666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 366.

The product of its digits is 6480, while the sum is 30.

The square root of 561666 is about 749.4437937564. The cubic root of 561666 is about 82.5073638973.

The spelling of 561666 in words is "five hundred sixty-one thousand, six hundred sixty-six".