665640839 has 2 divisors, whose sum is σ = 665640840. Its totient is φ = 665640838.

The previous prime is 665640823. The next prime is 665640883. The reversal of 665640839 is 938046566.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 665640839 - 2⁴ = 665640823 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 665640793 and 665640802.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (665640809) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332820419 + 332820420.

It is an arithmetic number, because the mean of its divisors is an integer number (332820420).

Almost surely, 2^665640839 is an apocalyptic number.

665640839 is a deficient number, since it is larger than the sum of its proper divisors (1).

665640839 is an equidigital number, since it uses as much as digits as its factorization.

665640839 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 933120, while the sum is 47.

The square root of 665640839 is about 25800.0162596848. The cubic root of 665640839 is about 873.1321632127.

The spelling of 665640839 in words is "six hundred sixty-five million, six hundred forty thousand, eight hundred thirty-nine".