643644 has 36 divisors (see below), whose sum is σ = 1714440. Its totient is φ = 203040.

The previous prime is 643639. The next prime is 643649. The reversal of 643644 is 446346.

It is a happy number.

643644 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (643639) and next prime (643649).

It is a tau number, because it is divible by the number of its divisors (36).

It is a nude number because it is divisible by every one of its digits.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643649) by changing a digit.

643644 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 214 + ... + 1154.

2⁶⁴³⁶⁴⁴ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 643644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (857220).

643644 is an abundant number, since it is smaller than the sum of its proper divisors (1070796).

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

643644 is a wasteful number, since it uses less digits than its factorization.

643644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 970 (or 965 counting only the distinct ones).

The product of its digits is 6912, while the sum is 27.

The square root of 643644 is about 802.2742673176. The cubic root of 643644 is about 86.3406356612.

The spelling of 643644 in words is "six hundred forty-three thousand, six hundred forty-four".