78521 has 4 divisors (see below), whose sum is σ = 79092. Its totient is φ = 77952.

The previous prime is 78517. The next prime is 78539. The reversal of 78521 is 12587.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12587 = 41 ⋅307.

It can be written as a sum of positive squares in 2 ways, for example, as 18496 + 60025 = 136^2 + 245^2 .

It is a cyclic number.

It is not a de Polignac number, because 78521 - 2² = 78517 is a prime.

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

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78511) 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, 65 + ... + 401.

It is an arithmetic number, because the mean of its divisors is an integer number (19773).

2⁷⁸⁵²¹ is an apocalyptic number.

It is an amenable number.

78521 is a deficient number, since it is larger than the sum of its proper divisors (571).

78521 is a wasteful number, since it uses less digits than its factorization.

78521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 570.

The product of its digits is 560, while the sum is 23.

The square root of 78521 is about 280.2159881234. The cubic root of 78521 is about 42.8215063546.

The spelling of 78521 in words is "seventy-eight thousand, five hundred twenty-one".