639645731 has 2 divisors, whose sum is σ = 639645732. Its totient is φ = 639645730.

The previous prime is 639645707. The next prime is 639645733. The reversal of 639645731 is 137546936.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-639645731 is a prime.

It is a super-2 number, since 2×639645731² = 818293322373048722, which contains 22 as substring.

Together with 639645733, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (639645733) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319822865 + 319822866.

It is an arithmetic number, because the mean of its divisors is an integer number (319822866).

Almost surely, 2^639645731 is an apocalyptic number.

639645731 is a deficient number, since it is larger than the sum of its proper divisors (1).

639645731 is an equidigital number, since it uses as much as digits as its factorization.

639645731 is an evil number, because the sum of its binary digits is even.

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

The square root of 639645731 is about 25291.2184562152. The cubic root of 639645731 is about 861.6148363674.

The spelling of 639645731 in words is "six hundred thirty-nine million, six hundred forty-five thousand, seven hundred thirty-one".