• 668 can be written using four 4's:

668 has 6 divisors (see below), whose sum is σ = 1176. Its totient is φ = 332.

The previous prime is 661. The next prime is 673. The reversal of 668 is 866.

668 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

668 is an esthetic number in base 8, because in such base its adjacent digits differ by 1.

It is an Ulam number.

It is a plaindrome in base 8, base 10, base 11, base 12, base 14 and base 16.

It is a nialpdrome in base 9.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661) by changing a digit.

668 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80 + ... + 87.

It is an arithmetic number, because the mean of its divisors is an integer number (196).

It is an amenable number.

668 is a deficient number, since it is larger than the sum of its proper divisors (508).

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

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

The sum of its prime factors is 171 (or 169 counting only the distinct ones).

The product of its digits is 288, while the sum is 20.

The square root of 668 is about 25.8456959666. The cubic root of 668 is about 8.7416246389.

It can be divided in two parts, 66 and 8, that multiplied together give a triangular number (528 = T_{32}).

The spelling of 668 in words is "six hundred sixty-eight", and thus it is an aban number and an oban number.

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