31661 has 4 divisors (see below), whose sum is σ = 36192. Its totient is φ = 27132.

The previous prime is 31657. The next prime is 31663. The reversal of 31661 is 16613.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 16613 = 37 ⋅449.

It is not a de Polignac number, because 31661 - 2² = 31657 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31663) 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 3 ways as a sum of consecutive naturals, for example, 2255 + ... + 2268.

It is an arithmetic number, because the mean of its divisors is an integer number (9048).

2³¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

31661 is a deficient number, since it is larger than the sum of its proper divisors (4531).

31661 is an equidigital number, since it uses as much as digits as its factorization.

31661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4530.

The product of its digits is 108, while the sum is 17.

The square root of 31661 is about 177.9353815294. The cubic root of 31661 is about 31.6355126044.

The spelling of 31661 in words is "thirty-one thousand, six hundred sixty-one".