667988921 has 2 divisors, whose sum is σ = 667988922. Its totient is φ = 667988920.

The previous prime is 667988917. The next prime is 667988927. The reversal of 667988921 is 129889766.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 667447225 + 541696 = 25835^2 + 736^2 .

It is a cyclic number.

It is not a de Polignac number, because 667988921 - 2² = 667988917 is a prime.

It is not a weakly prime, because it can be changed into another prime (667988927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333994460 + 333994461.

It is an arithmetic number, because the mean of its divisors is an integer number (333994461).

Almost surely, 2^667988921 is an apocalyptic number.

It is an amenable number.

667988921 is a deficient number, since it is larger than the sum of its proper divisors (1).

667988921 is an equidigital number, since it uses as much as digits as its factorization.

667988921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2612736, while the sum is 56.

The square root of 667988921 is about 25845.4816360617. The cubic root of 667988921 is about 874.1576311015.

The spelling of 667988921 in words is "six hundred sixty-seven million, nine hundred eighty-eight thousand, nine hundred twenty-one".