643750909 has 2 divisors, whose sum is σ = 643750910. Its totient is φ = 643750908.

The previous prime is 643750907. The next prime is 643750931. The reversal of 643750909 is 909057346.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 492706809 + 151044100 = 22197^2 + 12290^2 .

It is a cyclic number.

It is not a de Polignac number, because 643750909 - 2¹ = 643750907 is a prime.

Together with 643750907, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643750907) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321875454 + 321875455.

It is an arithmetic number, because the mean of its divisors is an integer number (321875455).

Almost surely, 2^643750909 is an apocalyptic number.

It is an amenable number.

643750909 is a deficient number, since it is larger than the sum of its proper divisors (1).

643750909 is an equidigital number, since it uses as much as digits as its factorization.

643750909 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 204120, while the sum is 43.

The square root of 643750909 is about 25372.2468260105. The cubic root of 643750909 is about 863.4541577773.

The spelling of 643750909 in words is "six hundred forty-three million, seven hundred fifty thousand, nine hundred nine".