643978 has 8 divisors (see below), whose sum is σ = 972900. Its totient is φ = 319680.

The previous prime is 643969. The next prime is 643991. The reversal of 643978 is 879346.

643978 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 2 ways, for example, as 628849 + 15129 = 793^2 + 123^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 783 + ... + 1378.

2⁶⁴³⁹⁷⁸ is an apocalyptic number.

643978 is a deficient number, since it is larger than the sum of its proper divisors (328922).

643978 is a wasteful number, since it uses less digits than its factorization.

643978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2312.

The product of its digits is 36288, while the sum is 37.

The square root of 643978 is about 802.4823985609. The cubic root of 643978 is about 86.3555677176.

The spelling of 643978 in words is "six hundred forty-three thousand, nine hundred seventy-eight".