816635221 has 4 divisors (see below), whose sum is σ = 818975500. Its totient is φ = 814294944.

The previous prime is 816635189. The next prime is 816635227. The reversal of 816635221 is 122536618.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 395811025 + 420824196 = 19895^2 + 20514^2 .

It is a cyclic number.

It is not a de Polignac number, because 816635221 - 2⁵ = 816635189 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (816635227) 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, 1169616 + ... + 1170313.

It is an arithmetic number, because the mean of its divisors is an integer number (204743875).

Almost surely, 2^816635221 is an apocalyptic number.

It is an amenable number.

816635221 is a deficient number, since it is larger than the sum of its proper divisors (2340279).

816635221 is a wasteful number, since it uses less digits than its factorization.

816635221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2340278.

The product of its digits is 17280, while the sum is 34.

The square root of 816635221 is about 28576.8301426173. The cubic root of 816635221 is about 934.7081632786.

The spelling of 816635221 in words is "eight hundred sixteen million, six hundred thirty-five thousand, two hundred twenty-one".