816815809 has 2 divisors, whose sum is σ = 816815810. Its totient is φ = 816815808.

The previous prime is 816815777. The next prime is 816815837. The reversal of 816815809 is 908518618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 726033025 + 90782784 = 26945^2 + 9528^2 .

It is a cyclic number.

It is not a de Polignac number, because 816815809 - 2⁵ = 816815777 is a prime.

It is not a weakly prime, because it can be changed into another prime (816815849) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 408407904 + 408407905.

It is an arithmetic number, because the mean of its divisors is an integer number (408407905).

Almost surely, 2^816815809 is an apocalyptic number.

It is an amenable number.

816815809 is a deficient number, since it is larger than the sum of its proper divisors (1).

816815809 is an equidigital number, since it uses as much as digits as its factorization.

816815809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 138240, while the sum is 46.

The square root of 816815809 is about 28579.9896605999. The cubic root of 816815809 is about 934.7770576199. Note that the first 3 decimals are identical.

The spelling of 816815809 in words is "eight hundred sixteen million, eight hundred fifteen thousand, eight hundred nine".