681785921 has 2 divisors, whose sum is σ = 681785922. Its totient is φ = 681785920.

The previous prime is 681785893. The next prime is 681785927. The reversal of 681785921 is 129587186.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 681784321 + 1600 = 26111^2 + 40^2 .

It is a cyclic number.

It is not a de Polignac number, because 681785921 - 2⁶ = 681785857 is a prime.

It is not a weakly prime, because it can be changed into another prime (681785927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340892960 + 340892961.

It is an arithmetic number, because the mean of its divisors is an integer number (340892961).

Almost surely, 2^681785921 is an apocalyptic number.

It is an amenable number.

681785921 is a deficient number, since it is larger than the sum of its proper divisors (1).

681785921 is an equidigital number, since it uses as much as digits as its factorization.

681785921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 241920, while the sum is 47.

The square root of 681785921 is about 26111.0306384103. The cubic root of 681785921 is about 880.1351036543.

The spelling of 681785921 in words is "six hundred eighty-one million, seven hundred eighty-five thousand, nine hundred twenty-one".