681991081 has 2 divisors, whose sum is σ = 681991082. Its totient is φ = 681991080.

The previous prime is 681991049. The next prime is 681991097. The reversal of 681991081 is 180199186.

It is a happy number.

681991081 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., 606144400 + 75846681 = 24620^2 + 8709^2 .

It is a cyclic number.

It is not a de Polignac number, because 681991081 - 2⁵ = 681991049 is a prime.

It is a super-2 number, since 2×681991081² = 930223669127097122, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (681991001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340995540 + 340995541.

It is an arithmetic number, because the mean of its divisors is an integer number (340995541).

Almost surely, 2^681991081 is an apocalyptic number.

It is an amenable number.

681991081 is a deficient number, since it is larger than the sum of its proper divisors (1).

681991081 is an equidigital number, since it uses as much as digits as its factorization.

681991081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 31104, while the sum is 43.

The square root of 681991081 is about 26114.9589507623. The cubic root of 681991081 is about 880.2233769198.

The spelling of 681991081 in words is "six hundred eighty-one million, nine hundred ninety-one thousand, eighty-one".