681321691 has 2 divisors, whose sum is σ = 681321692. Its totient is φ = 681321690.

The previous prime is 681321671. The next prime is 681321821. The reversal of 681321691 is 196123186.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 681321691 - 2¹⁷ = 681190619 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 681321691.

It is not a weakly prime, because it can be changed into another prime (681321601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340660845 + 340660846.

It is an arithmetic number, because the mean of its divisors is an integer number (340660846).

Almost surely, 2^681321691 is an apocalyptic number.

681321691 is a deficient number, since it is larger than the sum of its proper divisors (1).

681321691 is an equidigital number, since it uses as much as digits as its factorization.

681321691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 37.

The square root of 681321691 is about 26102.1395866316. The cubic root of 681321691 is about 879.9352961207.

The spelling of 681321691 in words is "six hundred eighty-one million, three hundred twenty-one thousand, six hundred ninety-one".