645863809 has 2 divisors, whose sum is σ = 645863810. Its totient is φ = 645863808.

The previous prime is 645863797. The next prime is 645863831. The reversal of 645863809 is 908368546.

It is a happy number.

645863809 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 384944400 + 260919409 = 19620^2 + 16153^2 .

It is a cyclic number.

It is not a de Polignac number, because 645863809 - 2⁷ = 645863681 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (645863839) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322931904 + 322931905.

It is an arithmetic number, because the mean of its divisors is an integer number (322931905).

Almost surely, 2^645863809 is an apocalyptic number.

It is an amenable number.

645863809 is a deficient number, since it is larger than the sum of its proper divisors (1).

645863809 is an equidigital number, since it uses as much as digits as its factorization.

645863809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1244160, while the sum is 49.

The square root of 645863809 is about 25413.8507314417. The cubic root of 645863809 is about 864.3977939506.

The spelling of 645863809 in words is "six hundred forty-five million, eight hundred sixty-three thousand, eight hundred nine".