643438656 has 168 divisors, whose sum is σ = 2148254784. Its totient is φ = 180311040.

The previous prime is 643438637. The next prime is 643438657. The reversal of 643438656 is 656834346.

It is a tau number, because it is divible by the number of its divisors (168).

It is not an unprimeable number, because it can be changed into a prime (643438657) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 212191 + ... + 215201.

Almost surely, 2^643438656 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 643438656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1074127392).

643438656 is an abundant number, since it is smaller than the sum of its proper divisors (1504816128).

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

643438656 is a wasteful number, since it uses less digits than its factorization.

643438656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3089 (or 3076 counting only the distinct ones).

The product of its digits is 1244160, while the sum is 45.

The square root of 643438656 is about 25366.0926435271. The cubic root of 643438656 is about 863.3145283276.

The spelling of 643438656 in words is "six hundred forty-three million, four hundred thirty-eight thousand, six hundred fifty-six".