643961664 has 168 divisors, whose sum is σ = 1957108608. Its totient is φ = 209848320.

The previous prime is 643961663. The next prime is 643961671. The reversal of 643961664 is 466169346.

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 (643961663) 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, 730504 + ... + 731384.

It is an arithmetic number, because the mean of its divisors is an integer number (11649456).

Almost surely, 2^643961664 is an apocalyptic number.

643961664 is a gapful number since it is divisible by the number (64) 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 643961664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (978554304).

643961664 is an abundant number, since it is smaller than the sum of its proper divisors (1313146944).

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

643961664 is an equidigital number, since it uses as much as digits as its factorization.

643961664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 955 (or 933 counting only the distinct ones).

The product of its digits is 559872, while the sum is 45.

The square root of 643961664 is about 25376.3997446446. The cubic root of 643961664 is about 863.5483750816.

The spelling of 643961664 in words is "six hundred forty-three million, nine hundred sixty-one thousand, six hundred sixty-four".