685767721 has 2 divisors, whose sum is σ = 685767722. Its totient is φ = 685767720.

The previous prime is 685767707. The next prime is 685767773. The reversal of 685767721 is 127767586.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 625550121 + 60217600 = 25011^2 + 7760^2 .

It is a cyclic number.

It is not a de Polignac number, because 685767721 - 2²⁹ = 148896809 is a prime.

It is not a weakly prime, because it can be changed into another prime (685767781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 342883860 + 342883861.

It is an arithmetic number, because the mean of its divisors is an integer number (342883861).

Almost surely, 2^685767721 is an apocalyptic number.

It is an amenable number.

685767721 is a deficient number, since it is larger than the sum of its proper divisors (1).

685767721 is an equidigital number, since it uses as much as digits as its factorization.

685767721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 987840, while the sum is 49.

The square root of 685767721 is about 26187.1671052827. The cubic root of 685767721 is about 881.8451817841.

The spelling of 685767721 in words is "six hundred eighty-five million, seven hundred sixty-seven thousand, seven hundred twenty-one".