678693721 has 2 divisors, whose sum is σ = 678693722. Its totient is φ = 678693720.

The previous prime is 678693667. The next prime is 678693731. The reversal of 678693721 is 127396876.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 430977600 + 247716121 = 20760^2 + 15739^2 .

It is a cyclic number.

It is not a de Polignac number, because 678693721 - 2¹⁵ = 678660953 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (678693731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 339346860 + 339346861.

It is an arithmetic number, because the mean of its divisors is an integer number (339346861).

Almost surely, 2^678693721 is an apocalyptic number.

It is an amenable number.

678693721 is a deficient number, since it is larger than the sum of its proper divisors (1).

678693721 is an equidigital number, since it uses as much as digits as its factorization.

678693721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 762048, while the sum is 49.

The square root of 678693721 is about 26051.7508240809. The cubic root of 678693721 is about 878.8024865944.

The spelling of 678693721 in words is "six hundred seventy-eight million, six hundred ninety-three thousand, seven hundred twenty-one".