643666 has 4 divisors (see below), whose sum is σ = 965502. Its totient is φ = 321832.

The previous prime is 643661. The next prime is 643681. The reversal of 643666 is 666346.

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

It can be written as a sum of positive squares in only one way, i.e., 531441 + 112225 = 729^2 + 335^2 .

It is not an unprimeable number, because it can be changed into a prime (643661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 160915 + ... + 160918.

2⁶⁴³⁶⁶⁶ is an apocalyptic number.

643666 is a deficient number, since it is larger than the sum of its proper divisors (321836).

643666 is a wasteful number, since it uses less digits than its factorization.

643666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 321835.

The product of its digits is 15552, while the sum is 31.

The square root of 643666 is about 802.2879782223. The cubic root of 643666 is about 86.3416193687.

The spelling of 643666 in words is "six hundred forty-three thousand, six hundred sixty-six".