643256640 has 560 divisors, whose sum is σ = 2602309248. Its totient is φ = 149630976.

The previous prime is 643256639. The next prime is 643256689. The reversal of 643256640 is 46652346.

643256640 is a `hidden beast` number, since 6 + 4 + 3 + 2 + 5 + 6 + 640 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 643256595 and 643256604.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 7750039 + ... + 7750121.

Almost surely, 2^643256640 is an apocalyptic number.

643256640 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 643256640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1301154624).

643256640 is an abundant number, since it is smaller than the sum of its proper divisors (1959052608).

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

643256640 is a wasteful number, since it uses less digits than its factorization.

643256640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 148 (or 129 counting only the distinct ones).

The product of its (nonzero) digits is 103680, while the sum is 36.

The square root of 643256640 is about 25362.5046081810. The cubic root of 643256640 is about 863.2331158132.

The spelling of 643256640 in words is "six hundred forty-three million, two hundred fifty-six thousand, six hundred forty".