681525721 has 2 divisors, whose sum is σ = 681525722. Its totient is φ = 681525720.

The previous prime is 681525703. The next prime is 681525727. The reversal of 681525721 is 127525186.

681525721 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., 588596121 + 92929600 = 24261^2 + 9640^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-681525721 is a prime.

It is not a weakly prime, because it can be changed into another prime (681525727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340762860 + 340762861.

It is an arithmetic number, because the mean of its divisors is an integer number (340762861).

Almost surely, 2^681525721 is an apocalyptic number.

It is an amenable number.

681525721 is a deficient number, since it is larger than the sum of its proper divisors (1).

681525721 is an equidigital number, since it uses as much as digits as its factorization.

681525721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 33600, while the sum is 37.

The square root of 681525721 is about 26106.0475943794. The cubic root of 681525721 is about 880.0231231011.

The spelling of 681525721 in words is "six hundred eighty-one million, five hundred twenty-five thousand, seven hundred twenty-one".