15561 has 24 divisors (see below), whose sum is σ = 29120. Its totient is φ = 7776.

The previous prime is 15559. The next prime is 15569. The reversal of 15561 is 16551.

15561 is nontrivially palindromic in base 12.

It is not a de Polignac number, because 15561 - 2¹ = 15559 is a prime.

It is a Curzon number.

It is a nialpdrome in base 5 and base 13.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 15561.

It is not an unprimeable number, because it can be changed into a prime (15569) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 810 + ... + 828.

2¹⁵⁵⁶¹ is an apocalyptic number.

It is an amenable number.

15561 is a deficient number, since it is larger than the sum of its proper divisors (13559).

15561 is a wasteful number, since it uses less digits than its factorization.

15561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 45 (or 42 counting only the distinct ones).

The product of its digits is 150, while the sum is 18.

The square root of 15561 is about 124.7437373178. The cubic root of 15561 is about 24.9658199569.

Subtracting 15561 from its reverse (16551), we obtain a triangular number (990 = T₄₄).

It can be divided in two parts, 155 and 61, that added together give a cube (216 = 6³).

The spelling of 15561 in words is "fifteen thousand, five hundred sixty-one".