816521 has 2 divisors, whose sum is σ = 816522. Its totient is φ = 816520.

The previous prime is 816499. The next prime is 816539. The reversal of 816521 is 125618.

816521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 546121 + 270400 = 739^2 + 520^2 .

It is a cyclic number.

It is not a de Polignac number, because 816521 - 2¹⁸ = 554377 is a prime.

It is a Sophie Germain prime.

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

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (816581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 408260 + 408261.

It is an arithmetic number, because the mean of its divisors is an integer number (408261).

2⁸¹⁶⁵²¹ is an apocalyptic number.

It is an amenable number.

816521 is a deficient number, since it is larger than the sum of its proper divisors (1).

816521 is an equidigital number, since it uses as much as digits as its factorization.

816521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 480, while the sum is 23.

The square root of 816521 is about 903.6155155817. The cubic root of 816521 is about 93.4664582711.

The spelling of 816521 in words is "eight hundred sixteen thousand, five hundred twenty-one".