5661 has 12 divisors (see below), whose sum is σ = 8892. Its totient is φ = 3456.

The previous prime is 5659. The next prime is 5669. The reversal of 5661 is 1665.

5661 is a `hidden beast` number, since 5 + 661 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 4761 + 900 = 69^2 + 30^2 .

It is not a de Polignac number, because 5661 - 2¹ = 5659 is a prime.

Its product of digits (180) is a multiple of the sum of its prime factors (60).

5661 is a lucky number.

It is a plaindrome in base 7 and base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (5669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 135 + ... + 171.

It is an arithmetic number, because the mean of its divisors is an integer number (741).

2⁵⁶⁶¹ is an apocalyptic number.

5661 is a gapful number since it is divisible by the number (51) formed by its first and last digit.

It is an amenable number.

5661 is a deficient number, since it is larger than the sum of its proper divisors (3231).

5661 is a wasteful number, since it uses less digits than its factorization.

5661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 60 (or 57 counting only the distinct ones).

The product of its digits is 180, while the sum is 18.

The square root of 5661 is about 75.2396172239. The cubic root of 5661 is about 17.8223260652.

It can be divided in two parts, 5 and 661, that added together give a palindrome (666).

The spelling of 5661 in words is "five thousand, six hundred sixty-one".