643988 has 6 divisors (see below), whose sum is σ = 1126986. Its totient is φ = 321992.

The previous prime is 643969. The next prime is 643991. The reversal of 643988 is 889346.

643988 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 643204 + 784 = 802^2 + 28^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80495 + ... + 80502.

It is an arithmetic number, because the mean of its divisors is an integer number (187831).

2⁶⁴³⁹⁸⁸ is an apocalyptic number.

It is an amenable number.

643988 is a deficient number, since it is larger than the sum of its proper divisors (482998).

643988 is a wasteful number, since it uses less digits than its factorization.

643988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 161001 (or 160999 counting only the distinct ones).

The product of its digits is 41472, while the sum is 38.

The square root of 643988 is about 802.4886292029. The cubic root of 643988 is about 86.3560147056.

The spelling of 643988 in words is "six hundred forty-three thousand, nine hundred eighty-eight".