18521 has 2 divisors, whose sum is σ = 18522. Its totient is φ = 18520.

The previous prime is 18517. The next prime is 18523. The reversal of 18521 is 12581.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18496 + 25 = 136^2 + 5^2 .

It is a cyclic number.

It is not a de Polignac number, because 18521 - 2² = 18517 is a prime.

Together with 18523, it forms a pair of twin primes.

It is a Chen prime.

It is an alternating number because its digits alternate between odd and even.

It is a nialpdrome in base 12.

It is a self number, because there is not a number n which added to its sum of digits gives 18521.

It is not a weakly prime, because it can be changed into another prime (18523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9260 + 9261.

It is an arithmetic number, because the mean of its divisors is an integer number (9261).

2¹⁸⁵²¹ is an apocalyptic number.

It is an amenable number.

18521 is a deficient number, since it is larger than the sum of its proper divisors (1).

18521 is an equidigital number, since it uses as much as digits as its factorization.

18521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 80, while the sum is 17.

The square root of 18521 is about 136.0918807277. The cubic root of 18521 is about 26.4578658786.

The spelling of 18521 in words is "eighteen thousand, five hundred twenty-one".