681939821 has 2 divisors, whose sum is σ = 681939822. Its totient is φ = 681939820.

The previous prime is 681939781. The next prime is 681939871. The reversal of 681939821 is 128939186.

681939821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 548074921 + 133864900 = 23411^2 + 11570^2 .

It is a cyclic number.

It is not a de Polignac number, because 681939821 - 2²² = 677745517 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (681939871) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340969910 + 340969911.

It is an arithmetic number, because the mean of its divisors is an integer number (340969911).

Almost surely, 2^681939821 is an apocalyptic number.

It is an amenable number.

681939821 is a deficient number, since it is larger than the sum of its proper divisors (1).

681939821 is an equidigital number, since it uses as much as digits as its factorization.

681939821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 186624, while the sum is 47.

The square root of 681939821 is about 26113.9775024794. The cubic root of 681939821 is about 880.2013231706.

The spelling of 681939821 in words is "six hundred eighty-one million, nine hundred thirty-nine thousand, eight hundred twenty-one".