643687642 has 16 divisors (see below), whose sum is σ = 1041315912. Its totient is φ = 296654400.

The previous prime is 643687613. The next prime is 643687651. The reversal of 643687642 is 246786346.

It is a Cunningham number, because it is equal to 25371²+1.

It can be written as a sum of positive squares in 4 ways, for example, as 555120721 + 88566921 = 23561^2 + 9411^2 .

It is a junction number, because it is equal to n+sod(n) for n = 643687592 and 643687601.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 568 + ... + 35884.

Almost surely, 2^643687642 is an apocalyptic number.

643687642 is a deficient number, since it is larger than the sum of its proper divisors (397628270).

643687642 is a wasteful number, since it uses less digits than its factorization.

643687642 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36033.

The product of its digits is 1161216, while the sum is 46.

The square root of 643687642 is about 25371.0000197075. Note that the first 4 decimals coincide. The cubic root of 643687642 is about 863.4258704677.

It can be divided in two parts, 64368 and 7642, that added together give a triangular number (72010 = T₃₇₉).

The spelling of 643687642 in words is "six hundred forty-three million, six hundred eighty-seven thousand, six hundred forty-two".