643646957 has 4 divisors (see below), whose sum is σ = 653253696. Its totient is φ = 634040220.

The previous prime is 643646921. The next prime is 643647007. The reversal of 643646957 is 759646346.

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 not a de Polignac number, because 643646957 - 2¹⁸ = 643384813 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643646917) 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 3 ways as a sum of consecutive naturals, for example, 4803269 + ... + 4803402.

It is an arithmetic number, because the mean of its divisors is an integer number (163313424).

Almost surely, 2^643646957 is an apocalyptic number.

643646957 is a gapful number since it is divisible by the number (67) formed by its first and last digit.

It is an amenable number.

643646957 is a deficient number, since it is larger than the sum of its proper divisors (9606739).

643646957 is an equidigital number, since it uses as much as digits as its factorization.

643646957 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9606738.

The product of its digits is 3265920, while the sum is 50.

The square root of 643646957 is about 25370.1982057689. The cubic root of 643646957 is about 863.4076788173.

The spelling of 643646957 in words is "six hundred forty-three million, six hundred forty-six thousand, nine hundred fifty-seven".