19561 has 4 divisors (see below), whose sum is σ = 20224. Its totient is φ = 18900.

The previous prime is 19559. The next prime is 19571. The reversal of 19561 is 16591.

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: 16591 = 47 ⋅353.

It is a cyclic number.

It is not a de Polignac number, because 19561 - 2¹ = 19559 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 3.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19501) 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, 285 + ... + 346.

It is an arithmetic number, because the mean of its divisors is an integer number (5056).

2¹⁹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

19561 is a deficient number, since it is larger than the sum of its proper divisors (663).

19561 is an equidigital number, since it uses as much as digits as its factorization.

19561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 662.

The product of its digits is 270, while the sum is 22.

The square root of 19561 is about 139.8606449292. The cubic root of 19561 is about 26.9441001676.

Subtracting from 19561 its product of digits (270), we obtain a palindrome (19291).

It can be divided in two parts, 195 and 61, that added together give a 8-th power (256 = 2⁸).

The spelling of 19561 in words is "nineteen thousand, five hundred sixty-one".