639280657 has 4 divisors (see below), whose sum is σ = 639398196. Its totient is φ = 639163120.

The previous prime is 639280639. The next prime is 639280679. The reversal of 639280657 is 756082936.

It is a Cunningham number, because it is equal to 25284²+1.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 372644416 + 266636241 = 19304^2 + 16329^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-639280657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639280627) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 50194 + ... + 61627.

It is an arithmetic number, because the mean of its divisors is an integer number (159849549).

Almost surely, 2^639280657 is an apocalyptic number.

It is an amenable number.

639280657 is a deficient number, since it is larger than the sum of its proper divisors (117539).

639280657 is a wasteful number, since it uses less digits than its factorization.

639280657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117538.

The product of its (nonzero) digits is 544320, while the sum is 46.

The square root of 639280657 is about 25284.0000197754. Note that the first 4 decimals coincide. The cubic root of 639280657 is about 861.4508846560.

The spelling of 639280657 in words is "six hundred thirty-nine million, two hundred eighty thousand, six hundred fifty-seven".