639691649 has 2 divisors, whose sum is σ = 639691650. Its totient is φ = 639691648.

The previous prime is 639691583. The next prime is 639691711. The reversal of 639691649 is 946196936.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 540888049 + 98803600 = 23257^2 + 9940^2 .

It is a cyclic number.

It is not a de Polignac number, because 639691649 - 2¹² = 639687553 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 639691649.

It is not a weakly prime, because it can be changed into another prime (639691049) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319845824 + 319845825.

It is an arithmetic number, because the mean of its divisors is an integer number (319845825).

Almost surely, 2^639691649 is an apocalyptic number.

It is an amenable number.

639691649 is a deficient number, since it is larger than the sum of its proper divisors (1).

639691649 is an equidigital number, since it uses as much as digits as its factorization.

639691649 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1889568, while the sum is 53.

The square root of 639691649 is about 25292.1262253690. The cubic root of 639691649 is about 861.6354533441.

The spelling of 639691649 in words is "six hundred thirty-nine million, six hundred ninety-one thousand, six hundred forty-nine".