639660209 has 2 divisors, whose sum is σ = 639660210. Its totient is φ = 639660208.

The previous prime is 639660157. The next prime is 639660257. The reversal of 639660209 is 902066936.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 445336609 + 194323600 = 21103^2 + 13940^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-639660209 is a prime.

It is not a weakly prime, because it can be changed into another prime (639662209) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319830104 + 319830105.

It is an arithmetic number, because the mean of its divisors is an integer number (319830105).

Almost surely, 2^639660209 is an apocalyptic number.

It is an amenable number.

639660209 is a deficient number, since it is larger than the sum of its proper divisors (1).

639660209 is an equidigital number, since it uses as much as digits as its factorization.

639660209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 104976, while the sum is 41.

The square root of 639660209 is about 25291.5046804258. The cubic root of 639660209 is about 861.6213370312.

The spelling of 639660209 in words is "six hundred thirty-nine million, six hundred sixty thousand, two hundred nine".