640671 has 4 divisors (see below), whose sum is σ = 854232. Its totient is φ = 427112.

The previous prime is 640669. The next prime is 640687. The reversal of 640671 is 176046.

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 640671 - 2¹ = 640669 is a prime.

It is a D-number.

640671 is a lucky number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640671.

It is not an unprimeable number, because it can be changed into a prime (640621) 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, 106776 + ... + 106781.

It is an arithmetic number, because the mean of its divisors is an integer number (213558).

2⁶⁴⁰⁶⁷¹ is an apocalyptic number.

640671 is a deficient number, since it is larger than the sum of its proper divisors (213561).

640671 is a wasteful number, since it uses less digits than its factorization.

640671 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213560.

The product of its (nonzero) digits is 1008, while the sum is 24.

The square root of 640671 is about 800.4192651355. The cubic root of 640671 is about 86.2074942837.

The spelling of 640671 in words is "six hundred forty thousand, six hundred seventy-one".