643675691 has 2 divisors, whose sum is σ = 643675692. Its totient is φ = 643675690.

The previous prime is 643675621. The next prime is 643675693. The reversal of 643675691 is 196576346.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643675691 is a prime.

Together with 643675693, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (643675693) 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 as a sum of consecutive naturals, namely, 321837845 + 321837846.

It is an arithmetic number, because the mean of its divisors is an integer number (321837846).

Almost surely, 2^643675691 is an apocalyptic number.

643675691 is a deficient number, since it is larger than the sum of its proper divisors (1).

643675691 is an equidigital number, since it uses as much as digits as its factorization.

643675691 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 816480, while the sum is 47.

The square root of 643675691 is about 25370.7644938027. The cubic root of 643675691 is about 863.4205268477.

The spelling of 643675691 in words is "six hundred forty-three million, six hundred seventy-five thousand, six hundred ninety-one".