643731840 has 128 divisors (see below), whose sum is σ = 2279944800. Its totient is φ = 171657216.

The previous prime is 643731839. The next prime is 643731853. The reversal of 643731840 is 48137346.

643731840 is a `hidden beast` number, since 643 + 7 + 3 + 1 + 8 + 4 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (128).

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 = 643731795 and 643731804.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1347 + ... + 35906.

Almost surely, 2^643731840 is an apocalyptic number.

643731840 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 643731840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1139972400).

643731840 is an abundant number, since it is smaller than the sum of its proper divisors (1636212960).

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

643731840 is a wasteful number, since it uses less digits than its factorization.

643731840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37281 (or 37263 counting only the distinct ones).

The product of its (nonzero) digits is 48384, while the sum is 36.

The square root of 643731840 is about 25371.8710386128. The cubic root of 643731840 is about 863.4456320315.

The spelling of 643731840 in words is "six hundred forty-three million, seven hundred thirty-one thousand, eight hundred forty".