643799978 has 12 divisors (see below), whose sum is σ = 981801990. Its totient is φ = 316619280.

The previous prime is 643799941. The next prime is 643799983. The reversal of 643799978 is 879997346.

It can be written as a sum of positive squares in 3 ways, for example, as 112635769 + 531164209 = 10613^2 + 23047^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 643799978.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 35813 + ... + 50696.

Almost surely, 2^643799978 is an apocalyptic number.

643799978 is a deficient number, since it is larger than the sum of its proper divisors (338002012).

643799978 is an equidigital number, since it uses as much as digits as its factorization.

643799978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86633 (or 86572 counting only the distinct ones).

The product of its digits is 20575296, while the sum is 62.

The square root of 643799978 is about 25373.2137893488. The cubic root of 643799978 is about 863.4760957428.

The spelling of 643799978 in words is "six hundred forty-three million, seven hundred ninety-nine thousand, nine hundred seventy-eight".