643968 has 96 divisors (see below), whose sum is σ = 2042040. Its totient is φ = 193536.

The previous prime is 643961. The next prime is 643969. The reversal of 643968 is 869346.

643968 is a `hidden beast` number, since 643 + 9 + 6 + 8 = 666.

It is a tau number, because it is divible by the number of its divisors (96).

It is a Harshad number since it is a multiple of its sum of digits (36).

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

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643961) by changing a digit.

643968 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, 14955 + ... + 14997.

2⁶⁴³⁹⁶⁸ 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 643968, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1021020).

643968 is an abundant number, since it is smaller than the sum of its proper divisors (1398072).

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

643968 is a wasteful number, since it uses less digits than its factorization.

643968 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 76 (or 61 counting only the distinct ones).

The product of its digits is 31104, while the sum is 36.

The square root of 643968 is about 802.4761678704. The cubic root of 643968 is about 86.3551207250.

The spelling of 643968 in words is "six hundred forty-three thousand, nine hundred sixty-eight".