19521 has 10 divisors (see below), whose sum is σ = 29282. Its totient is φ = 12960.

The previous prime is 19507. The next prime is 19531. The reversal of 19521 is 12591.

It can be written as a sum of positive squares in only one way, i.e., 18225 + 1296 = 135^2 + 36^2 .

It is not a de Polignac number, because 19521 - 2⁵ = 19489 is a prime.

It is a Duffinian number.

It is a Curzon number.

19521 is a lucky number.

It is a nialpdrome in base 3.

It is a junction number, because it is equal to n+sod(n) for n = 19494 and 19503.

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 (5) of ones.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 40 + ... + 201.

It is a 2-hyperperfect number.

2¹⁹⁵²¹ is an apocalyptic number.

19521 is the 81-st octagonal number.

It is an amenable number.

19521 is a deficient number, since it is larger than the sum of its proper divisors (9761).

19521 is an equidigital number, since it uses as much as digits as its factorization.

19521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 253 (or 244 counting only the distinct ones).

The product of its digits is 90, while the sum is 18.

The square root of 19521 is about 139.7175722663. The cubic root of 19521 is about 26.9257217705.

Subtracting from 19521 its sum of digits (18), we obtain a triangular number (19503 = T₁₉₇).

It can be divided in two parts, 1952 and 1, that added together give a triangular number (1953 = T₆₂).

The spelling of 19521 in words is "nineteen thousand, five hundred twenty-one".