639660257 has 2 divisors, whose sum is σ = 639660258. Its totient is φ = 639660256.

The previous prime is 639660209. The next prime is 639660331. The reversal of 639660257 is 752066936.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 639533521 + 126736 = 25289^2 + 356^2 .

It is a cyclic number.

It is not a de Polignac number, because 639660257 - 2²⁶ = 572551393 is a prime.

It is not a weakly prime, because it can be changed into another prime (639660157) 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, 319830128 + 319830129.

It is an arithmetic number, because the mean of its divisors is an integer number (319830129).

Almost surely, 2^639660257 is an apocalyptic number.

It is an amenable number.

639660257 is a deficient number, since it is larger than the sum of its proper divisors (1).

639660257 is an equidigital number, since it uses as much as digits as its factorization.

639660257 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 408240, while the sum is 44.

The square root of 639660257 is about 25291.5056293610. The cubic root of 639660257 is about 861.6213585832.

The spelling of 639660257 in words is "six hundred thirty-nine million, six hundred sixty thousand, two hundred fifty-seven".