678721 has 2 divisors, whose sum is σ = 678722. Its totient is φ = 678720.

The previous prime is 678719. The next prime is 678731. The reversal of 678721 is 127876.

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., 408321 + 270400 = 639^2 + 520^2 .

It is a cyclic number.

It is not a de Polignac number, because 678721 - 2¹ = 678719 is a prime.

Together with 678719, it forms a pair of twin primes.

It is a Chen prime.

It is an Ulam number.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (678731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 339360 + 339361.

It is an arithmetic number, because the mean of its divisors is an integer number (339361).

2⁶⁷⁸⁷²¹ is an apocalyptic number.

It is an amenable number.

678721 is a deficient number, since it is larger than the sum of its proper divisors (1).

678721 is an equidigital number, since it uses as much as digits as its factorization.

678721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4704, while the sum is 31.

The square root of 678721 is about 823.8452524595. The cubic root of 678721 is about 87.8814260453.

The spelling of 678721 in words is "six hundred seventy-eight thousand, seven hundred twenty-one".