645668509 has 2 divisors, whose sum is σ = 645668510. Its totient is φ = 645668508.

The previous prime is 645668503. The next prime is 645668519. The reversal of 645668509 is 905866546.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 644042884 + 1625625 = 25378^2 + 1275^2 .

It is a cyclic number.

It is not a de Polignac number, because 645668509 - 2²⁹ = 108797597 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (645668503) 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, 322834254 + 322834255.

It is an arithmetic number, because the mean of its divisors is an integer number (322834255).

Almost surely, 2^645668509 is an apocalyptic number.

It is an amenable number.

645668509 is a deficient number, since it is larger than the sum of its proper divisors (1).

645668509 is an equidigital number, since it uses as much as digits as its factorization.

645668509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1555200, while the sum is 49.

The square root of 645668509 is about 25410.0080480113. The cubic root of 645668509 is about 864.3106579809.

The spelling of 645668509 in words is "six hundred forty-five million, six hundred sixty-eight thousand, five hundred nine".