643828781 has 8 divisors (see below), whose sum is σ = 668824128. Its totient is φ = 619276000.

The previous prime is 643828741. The next prime is 643828807. The reversal of 643828781 is 187828346.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 643828781 - 2²² = 639634477 is a prime.

It is a super-2 number, since 2×643828781² = 829030998487891922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643828711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 107675 + ... + 113496.

It is an arithmetic number, because the mean of its divisors is an integer number (83603016).

Almost surely, 2^643828781 is an apocalyptic number.

643828781 is the 11348-th centered decagonal number.

It is an amenable number.

643828781 is a deficient number, since it is larger than the sum of its proper divisors (24995347).

643828781 is a wasteful number, since it uses less digits than its factorization.

643828781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 221283.

The product of its digits is 516096, while the sum is 47.

The square root of 643828781 is about 25373.7813697525. The cubic root of 643828781 is about 863.4889725844.

The spelling of 643828781 in words is "six hundred forty-three million, eight hundred twenty-eight thousand, seven hundred eighty-one".