643817 has 4 divisors (see below), whose sum is σ = 647556. Its totient is φ = 640080.

The previous prime is 643781. The next prime is 643847. The reversal of 643817 is 718346.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 33856 + 609961 = 184^2 + 781^2 .

It is a cyclic number.

It is not a de Polignac number, because 643817 - 2¹⁴ = 627433 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 643817.

It is not an unprimeable number, because it can be changed into a prime (643847) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1598 + ... + 1959.

It is an arithmetic number, because the mean of its divisors is an integer number (161889).

2⁶⁴³⁸¹⁷ is an apocalyptic number.

It is an amenable number.

643817 is a deficient number, since it is larger than the sum of its proper divisors (3739).

643817 is a wasteful number, since it uses less digits than its factorization.

643817 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3738.

The product of its digits is 4032, while the sum is 29.

The square root of 643817 is about 802.3820785636. The cubic root of 643817 is about 86.3483705746.

Subtracting 643817 from its reverse (718346), we obtain a square (74529 = 273²).

The spelling of 643817 in words is "six hundred forty-three thousand, eight hundred seventeen".