17561 has 4 divisors (see below), whose sum is σ = 18612. Its totient is φ = 16512.

The previous prime is 17551. The next prime is 17569. The reversal of 17561 is 16571.

17561 = 4² + 5² + ... + 37².

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16571 = 73 ⋅227.

It can be written as a sum of positive squares in 2 ways, for example, as 15625 + 1936 = 125^2 + 44^2 .

It is a cyclic number.

It is not a de Polignac number, because 17561 - 2⁶ = 17497 is a prime.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a zygodrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (17569) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 500 + ... + 533.

It is an arithmetic number, because the mean of its divisors is an integer number (4653).

2¹⁷⁵⁶¹ is an apocalyptic number.

It is an amenable number.

17561 is a deficient number, since it is larger than the sum of its proper divisors (1051).

17561 is a wasteful number, since it uses less digits than its factorization.

17561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1050.

The product of its digits is 210, while the sum is 20.

The square root of 17561 is about 132.5179233161. The cubic root of 17561 is about 25.9926014452.

Adding to 17561 its product of digits (210), we get a palindrome (17771).

Subtracting from 17561 its reverse (16571), we obtain a triangular number (990 = T₄₄).

The spelling of 17561 in words is "seventeen thousand, five hundred sixty-one".