816831221 has 2 divisors, whose sum is σ = 816831222. Its totient is φ = 816831220.

The previous prime is 816831217. The next prime is 816831227. The reversal of 816831221 is 122138618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 813048196 + 3783025 = 28514^2 + 1945^2 .

It is a cyclic number.

It is not a de Polignac number, because 816831221 - 2² = 816831217 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (816831227) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 408415610 + 408415611.

It is an arithmetic number, because the mean of its divisors is an integer number (408415611).

Almost surely, 2^816831221 is an apocalyptic number.

It is an amenable number.

816831221 is a deficient number, since it is larger than the sum of its proper divisors (1).

816831221 is an equidigital number, since it uses as much as digits as its factorization.

816831221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4608, while the sum is 32.

The square root of 816831221 is about 28580.2592885369. The cubic root of 816831221 is about 934.7829368293.

Adding to 816831221 its reverse (122138618), we get a palindrome (938969839).

The spelling of 816831221 in words is "eight hundred sixteen million, eight hundred thirty-one thousand, two hundred twenty-one".