666613921 has 2 divisors, whose sum is σ = 666613922. Its totient is φ = 666613920.

The previous prime is 666613901. The next prime is 666613949. The reversal of 666613921 is 129316666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 567392400 + 99221521 = 23820^2 + 9961^2 .

It is a cyclic number.

It is not a de Polignac number, because 666613921 - 2¹¹ = 666611873 is a prime.

It is not a weakly prime, because it can be changed into another prime (666613901) 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, 333306960 + 333306961.

It is an arithmetic number, because the mean of its divisors is an integer number (333306961).

Almost surely, 2^666613921 is an apocalyptic number.

It is an amenable number.

666613921 is a deficient number, since it is larger than the sum of its proper divisors (1).

666613921 is an equidigital number, since it uses as much as digits as its factorization.

666613921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 69984, while the sum is 40.

The square root of 666613921 is about 25818.8675390692. The cubic root of 666613921 is about 873.5574253367.

The spelling of 666613921 in words is "six hundred sixty-six million, six hundred thirteen thousand, nine hundred twenty-one".