681563809 has 2 divisors, whose sum is σ = 681563810. Its totient is φ = 681563808.

The previous prime is 681563783. The next prime is 681563837. The reversal of 681563809 is 908365186.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 515153809 + 166410000 = 22697^2 + 12900^2 .

It is a cyclic number.

It is not a de Polignac number, because 681563809 - 2⁵ = 681563777 is a prime.

It is not a weakly prime, because it can be changed into another prime (681560809) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340781904 + 340781905.

It is an arithmetic number, because the mean of its divisors is an integer number (340781905).

Almost surely, 2^681563809 is an apocalyptic number.

It is an amenable number.

681563809 is a deficient number, since it is larger than the sum of its proper divisors (1).

681563809 is an equidigital number, since it uses as much as digits as its factorization.

681563809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 311040, while the sum is 46.

The square root of 681563809 is about 26106.7770703318. Note that the first 3 decimals coincide. The cubic root of 681563809 is about 880.0395165623.

The spelling of 681563809 in words is "six hundred eighty-one million, five hundred sixty-three thousand, eight hundred nine".