643546991 has 2 divisors, whose sum is σ = 643546992. Its totient is φ = 643546990.

The previous prime is 643546979. The next prime is 643546999. The reversal of 643546991 is 199645346.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643546991 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643546999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321773495 + 321773496.

It is an arithmetic number, because the mean of its divisors is an integer number (321773496).

Almost surely, 2^643546991 is an apocalyptic number.

643546991 is a deficient number, since it is larger than the sum of its proper divisors (1).

643546991 is an equidigital number, since it uses as much as digits as its factorization.

643546991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 699840, while the sum is 47.

The square root of 643546991 is about 25368.2279830500. The cubic root of 643546991 is about 863.3629773549.

The spelling of 643546991 in words is "six hundred forty-three million, five hundred forty-six thousand, nine hundred ninety-one".