640947 has 4 divisors (see below), whose sum is σ = 854600. Its totient is φ = 427296.

The previous prime is 640943. The next prime is 640949. The reversal of 640947 is 749046.

640947 is nontrivially palindromic in base 15.

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

It is not a de Polignac number, because 640947 - 2² = 640943 is a prime.

It is a D-number.

It is a Duffinian number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640947.

It is not an unprimeable number, because it can be changed into a prime (640943) 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, 106822 + ... + 106827.

It is an arithmetic number, because the mean of its divisors is an integer number (213650).

2⁶⁴⁰⁹⁴⁷ is an apocalyptic number.

640947 is a deficient number, since it is larger than the sum of its proper divisors (213653).

640947 is a wasteful number, since it uses less digits than its factorization.

640947 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213652.

The product of its (nonzero) digits is 6048, while the sum is 30.

The square root of 640947 is about 800.5916562143. The cubic root of 640947 is about 86.2198718548.

The spelling of 640947 in words is "six hundred forty thousand, nine hundred forty-seven".