640543679 has 4 divisors (see below), whose sum is σ = 641681976. Its totient is φ = 639405384.

The previous prime is 640543649. The next prime is 640543681. The reversal of 640543679 is 976345046.

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 640543679 - 2¹⁶ = 640478143 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640543649) 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, 568304 + ... + 569429.

It is an arithmetic number, because the mean of its divisors is an integer number (160420494).

Almost surely, 2^640543679 is an apocalyptic number.

640543679 is a deficient number, since it is larger than the sum of its proper divisors (1138297).

640543679 is a wasteful number, since it uses less digits than its factorization.

640543679 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1138296.

The product of its (nonzero) digits is 544320, while the sum is 44.

The square root of 640543679 is about 25308.9643999908. The cubic root of 640543679 is about 862.0178321327.

The spelling of 640543679 in words is "six hundred forty million, five hundred forty-three thousand, six hundred seventy-nine".