643687641 has 15 divisors (see below), whose sum is σ = 961899301. Its totient is φ = 428972868.

The previous prime is 643687613. The next prime is 643687651. The reversal of 643687641 is 146786346.

It is a happy number.

The square root of 643687641 is 25371.

It is a perfect power (a square), and thus also a powerful number.

It is not a de Polignac number, because 643687641 - 2¹⁵ = 643654873 is a prime.

It is a super-2 number, since 2×643687641² = 828667558352289762, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (643687651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 226930 + ... + 229748.

Almost surely, 2^643687641 is an apocalyptic number.

643687641 is the 25371-st square number.

643687641 is the 12686-th centered octagonal number.

It is an amenable number.

643687641 is a deficient number, since it is larger than the sum of its proper divisors (318211660).

643687641 is an frugal number, since it uses more digits than its factorization.

643687641 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5650 (or 2822 counting only the distinct ones).

The product of its digits is 580608, while the sum is 45.

The cubic root of 643687641 is about 863.4258700206.

The spelling of 643687641 in words is "six hundred forty-three million, six hundred eighty-seven thousand, six hundred forty-one".