561661 has 8 divisors (see below), whose sum is σ = 582624. Its totient is φ = 541200.

The previous prime is 561607. The next prime is 561667. The reversal of 561661 is 166165.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 561661 - 2¹⁷ = 430589 is a prime.

It is a Duffinian number.

It is a congruent number.

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

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5511 + ... + 5611.

It is an arithmetic number, because the mean of its divisors is an integer number (72828).

2⁵⁶¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

561661 is a deficient number, since it is larger than the sum of its proper divisors (20963).

561661 is a wasteful number, since it uses less digits than its factorization.

561661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 251.

The product of its digits is 1080, while the sum is 25.

The square root of 561661 is about 749.4404579418. The cubic root of 561661 is about 82.5071190673.

The spelling of 561661 in words is "five hundred sixty-one thousand, six hundred sixty-one".