11561 has 4 divisors (see below), whose sum is σ = 12624. Its totient is φ = 10500.

The previous prime is 11551. The next prime is 11579. The reversal of 11561 is 16511.

11561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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.

It is a cyclic number.

It is not a de Polignac number, because 11561 - 2⁶ = 11497 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 5 and base 11.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 11561.

It is not an unprimeable number, because it can be changed into a prime (11551) 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 3 ways as a sum of consecutive naturals, for example, 515 + ... + 536.

It is an arithmetic number, because the mean of its divisors is an integer number (3156).

2¹¹⁵⁶¹ is an apocalyptic number.

11561 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

11561 is a deficient number, since it is larger than the sum of its proper divisors (1063).

11561 is a wasteful number, since it uses less digits than its factorization.

11561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1062.

The product of its digits is 30, while the sum is 14.

The square root of 11561 is about 107.5220907535. The cubic root of 11561 is about 22.6116263566.

Subtracting 11561 from its reverse (16511), we obtain a triangular number (4950 = T₉₉).

The spelling of 11561 in words is "eleven thousand, five hundred sixty-one".