643967 has 4 divisors (see below), whose sum is σ = 677880. Its totient is φ = 610056.

The previous prime is 643961. The next prime is 643969. The reversal of 643967 is 769346.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 769346 = 2 ⋅384673.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643967 is a prime.

It is a Duffinian 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.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16928 + ... + 16965.

It is an arithmetic number, because the mean of its divisors is an integer number (169470).

2⁶⁴³⁹⁶⁷ is an apocalyptic number.

643967 is a deficient number, since it is larger than the sum of its proper divisors (33913).

643967 is a wasteful number, since it uses less digits than its factorization.

643967 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33912.

The product of its digits is 27216, while the sum is 35.

The square root of 643967 is about 802.4755447987. The cubic root of 643967 is about 86.3550760255.

The spelling of 643967 in words is "six hundred forty-three thousand, nine hundred sixty-seven".