643687128 has 192 divisors, whose sum is σ = 2116159200. Its totient is φ = 180714240.

The previous prime is 643687127. The next prime is 643687147. The reversal of 643687128 is 821786346.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643687123) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 645126 + ... + 646122.

Almost surely, 2^643687128 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 643687128, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1058079600).

643687128 is an abundant number, since it is smaller than the sum of its proper divisors (1472472072).

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

643687128 is a wasteful number, since it uses less digits than its factorization.

643687128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1087 (or 1070 counting only the distinct ones).

The product of its digits is 387072, while the sum is 45.

The square root of 643687128 is about 25370.9898900299. The cubic root of 643687128 is about 863.4256406456.

The spelling of 643687128 in words is "six hundred forty-three million, six hundred eighty-seven thousand, one hundred twenty-eight".