643640 has 16 divisors (see below), whose sum is σ = 1448280. Its totient is φ = 257440.

The previous prime is 643639. The next prime is 643649. The reversal of 643640 is 46346.

It is a nialpdrome in base 15.

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 643640.

It is not an unprimeable number, because it can be changed into a prime (643649) 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, 8006 + ... + 8085.

2⁶⁴³⁶⁴⁰ is an apocalyptic number.

It is an amenable number.

643640 is an abundant number, since it is smaller than the sum of its proper divisors (804640).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

643640 is a wasteful number, since it uses less digits than its factorization.

643640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16102 (or 16098 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 23.

The square root of 643640 is about 802.2717744007. The cubic root of 643640 is about 86.3404568029.

Adding to 643640 its reverse (46346), we get a palindrome (689986).

The spelling of 643640 in words is "six hundred forty-three thousand, six hundred forty".