640247639 has 4 divisors (see below), whose sum is σ = 643282200. Its totient is φ = 637213080.

The previous prime is 640247611. The next prime is 640247651. The reversal of 640247639 is 936742046.

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

It is a cyclic number.

It is not a de Polignac number, because 640247639 - 2¹² = 640243543 is a prime.

It is a super-4 number, since 4×640247639⁴ (a number of 36 digits) contains 4444 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 640247596 and 640247605.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640247609) 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, 1516964 + ... + 1517385.

It is an arithmetic number, because the mean of its divisors is an integer number (160820550).

Almost surely, 2^640247639 is an apocalyptic number.

640247639 is a deficient number, since it is larger than the sum of its proper divisors (3034561).

640247639 is a wasteful number, since it uses less digits than its factorization.

640247639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3034560.

The product of its (nonzero) digits is 217728, while the sum is 41.

The square root of 640247639 is about 25303.1152034685. The cubic root of 640247639 is about 861.8850121073.

The spelling of 640247639 in words is "six hundred forty million, two hundred forty-seven thousand, six hundred thirty-nine".