561681 has 16 divisors (see below), whose sum is σ = 846720. Its totient is φ = 367920.

The previous prime is 561667. The next prime is 561703. The reversal of 561681 is 186165.

It is not a de Polignac number, because 561681 - 2⁷ = 561553 is a prime.

It is a super-2 number, since 2×561681² = 630971091522, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

561681 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (561181) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1771 + ... + 2063.

It is an arithmetic number, because the mean of its divisors is an integer number (52920).

2⁵⁶¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

561681 is a deficient number, since it is larger than the sum of its proper divisors (285039).

561681 is a wasteful number, since it uses less digits than its factorization.

561681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 373 (or 367 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 561681 is about 749.4538011112. The cubic root of 561681 is about 82.5080983786.

It can be divided in two parts, 56168 and 1, that added together give a square (56169 = 237²).

The spelling of 561681 in words is "five hundred sixty-one thousand, six hundred eighty-one".