68309721 has 6 divisors (see below), whose sum is σ = 98669610. Its totient is φ = 45539808.

The previous prime is 68309713. The next prime is 68309749. The reversal of 68309721 is 12790386.

It can be written as a sum of positive squares in only one way, i.e., 67568400 + 741321 = 8220^2 + 861^2 .

It is not a de Polignac number, because 68309721 - 2³ = 68309713 is a prime.

It is not an unprimeable number, because it can be changed into a prime (68309821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3794976 + ... + 3794993.

It is an arithmetic number, because the mean of its divisors is an integer number (16444935).

Almost surely, 2^68309721 is an apocalyptic number.

It is an amenable number.

68309721 is a deficient number, since it is larger than the sum of its proper divisors (30359889).

68309721 is a wasteful number, since it uses less digits than its factorization.

68309721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7589975 (or 7589972 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 68309721 is about 8264.9695099256. The cubic root of 68309721 is about 408.7842650062.

The spelling of 68309721 in words is "sixty-eight million, three hundred nine thousand, seven hundred twenty-one".