666640813 has 2 divisors, whose sum is σ = 666640814. Its totient is φ = 666640812.

The previous prime is 666640769. The next prime is 666640817. The reversal of 666640813 is 318046666.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 488498404 + 178142409 = 22102^2 + 13347^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-666640813 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666640817) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333320406 + 333320407.

It is an arithmetic number, because the mean of its divisors is an integer number (333320407).

Almost surely, 2^666640813 is an apocalyptic number.

It is an amenable number.

666640813 is a deficient number, since it is larger than the sum of its proper divisors (1).

666640813 is an equidigital number, since it uses as much as digits as its factorization.

666640813 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 124416, while the sum is 40.

The square root of 666640813 is about 25819.3883157599. The cubic root of 666640813 is about 873.5691719612.

The spelling of 666640813 in words is "six hundred sixty-six million, six hundred forty thousand, eight hundred thirteen".