81521 has 4 divisors (see below), whose sum is σ = 88944. Its totient is φ = 74100.

The previous prime is 81517. The next prime is 81527. The reversal of 81521 is 12518.

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 81521 - 2² = 81517 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81521.

It is not an unprimeable number, because it can be changed into a prime (81527) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3695 + ... + 3716.

It is an arithmetic number, because the mean of its divisors is an integer number (22236).

2⁸¹⁵²¹ is an apocalyptic number.

It is an amenable number.

81521 is a deficient number, since it is larger than the sum of its proper divisors (7423).

81521 is a wasteful number, since it uses less digits than its factorization.

81521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7422.

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

The square root of 81521 is about 285.5188259993. The cubic root of 81521 is about 43.3600558384.

The spelling of 81521 in words is "eighty-one thousand, five hundred twenty-one".