17661 has 12 divisors (see below), whose sum is σ = 27872. Its totient is φ = 9744.

The previous prime is 17659. The next prime is 17669. The reversal of 17661 is 16671.

It is not a de Polignac number, because 17661 - 2¹ = 17659 is a prime.

It is a hoax number, since the sum of its digits (21) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (17669) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 595 + ... + 623.

2¹⁷⁶⁶¹ is an apocalyptic number.

It is an amenable number.

17661 is a deficient number, since it is larger than the sum of its proper divisors (10211).

17661 is an equidigital number, since it uses as much as digits as its factorization.

17661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68 (or 39 counting only the distinct ones).

The product of its digits is 252, while the sum is 21.

The square root of 17661 is about 132.8946951537. The cubic root of 17661 is about 26.0418458299.

Multiplying 17661 by its sum of digits (21), we get a square (370881 = 609²).

17661 divided by its sum of digits (21) gives a square (841 = 29²).

Subtracting from 17661 its reverse (16671), we obtain a triangular number (990 = T₄₄).

The spelling of 17661 in words is "seventeen thousand, six hundred sixty-one".