643917640 has 32 divisors (see below), whose sum is σ = 1449637560. Its totient is φ = 257420800.

The previous prime is 643917613. The next prime is 643917643. The reversal of 643917640 is 46719346.

It can be written as a sum of positive squares in 4 ways, for example, as 387853636 + 256064004 = 19694^2 + 16002^2 .

It is a Harshad number since it is a multiple of its sum of digits (40).

It is a junction number, because it is equal to n+sod(n) for n = 643917593 and 643917602.

It is not an unprimeable number, because it can be changed into a prime (643917643) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 91860 + ... + 98620.

Almost surely, 2^643917640 is an apocalyptic number.

It is an amenable number.

643917640 is an abundant number, since it is smaller than the sum of its proper divisors (805719920).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

643917640 is a wasteful number, since it uses less digits than its factorization.

643917640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9153 (or 9149 counting only the distinct ones).

The product of its (nonzero) digits is 108864, while the sum is 40.

The square root of 643917640 is about 25375.5323096876. The cubic root of 643917640 is about 863.5286960012.

The spelling of 643917640 in words is "six hundred forty-three million, nine hundred seventeen thousand, six hundred forty".