681305921 has 2 divisors, whose sum is σ = 681305922. Its totient is φ = 681305920.

The previous prime is 681305893. The next prime is 681305929. The reversal of 681305921 is 129503186.

681305921 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., 351375025 + 329930896 = 18745^2 + 18164^2 .

It is a cyclic number.

It is not a de Polignac number, because 681305921 - 2²⁶ = 614197057 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (681305929) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340652960 + 340652961.

It is an arithmetic number, because the mean of its divisors is an integer number (340652961).

Almost surely, 2^681305921 is an apocalyptic number.

It is an amenable number.

681305921 is a deficient number, since it is larger than the sum of its proper divisors (1).

681305921 is an equidigital number, since it uses as much as digits as its factorization.

681305921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 12960, while the sum is 35.

The square root of 681305921 is about 26101.8375023675. The cubic root of 681305921 is about 879.9285070191.

The spelling of 681305921 in words is "six hundred eighty-one million, three hundred five thousand, nine hundred twenty-one".