643580981 has 4 divisors (see below), whose sum is σ = 648211200. Its totient is φ = 638950764.

The previous prime is 643580947. The next prime is 643580999. The reversal of 643580981 is 189085346.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643580981 is a prime.

It is a super-2 number, since 2×643580981² = 828392958209844722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643580911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2314901 + ... + 2315178.

It is an arithmetic number, because the mean of its divisors is an integer number (162052800).

Almost surely, 2^643580981 is an apocalyptic number.

It is an amenable number.

643580981 is a deficient number, since it is larger than the sum of its proper divisors (4630219).

643580981 is a wasteful number, since it uses less digits than its factorization.

643580981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4630218.

The product of its (nonzero) digits is 207360, while the sum is 44.

The square root of 643580981 is about 25368.8979066888. The cubic root of 643580981 is about 863.3781770690.

The spelling of 643580981 in words is "six hundred forty-three million, five hundred eighty thousand, nine hundred eighty-one".