643997 has 4 divisors (see below), whose sum is σ = 651840. Its totient is φ = 636156.

The previous prime is 643991. The next prime is 644009. The reversal of 643997 is 799346.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 643997 - 2¹⁰ = 642973 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 643997.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643991) 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, 3797 + ... + 3962.

It is an arithmetic number, because the mean of its divisors is an integer number (162960).

2⁶⁴³⁹⁹⁷ is an apocalyptic number.

It is an amenable number.

643997 is a deficient number, since it is larger than the sum of its proper divisors (7843).

643997 is an equidigital number, since it uses as much as digits as its factorization.

643997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7842.

The product of its digits is 40824, while the sum is 38.

The square root of 643997 is about 802.4942367394. The cubic root of 643997 is about 86.3564169908.

The spelling of 643997 in words is "six hundred forty-three thousand, nine hundred ninety-seven".