645680309 has 2 divisors, whose sum is σ = 645680310. Its totient is φ = 645680308.

The previous prime is 645680297. The next prime is 645680333. The reversal of 645680309 is 903086546.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 600495025 + 45185284 = 24505^2 + 6722^2 .

It is a cyclic number.

It is not a de Polignac number, because 645680309 - 2⁴ = 645680293 is a prime.

It is a super-2 number, since 2×645680309² = 833806122860670962, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (645680359) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322840154 + 322840155.

It is an arithmetic number, because the mean of its divisors is an integer number (322840155).

Almost surely, 2^645680309 is an apocalyptic number.

It is an amenable number.

645680309 is a deficient number, since it is larger than the sum of its proper divisors (1).

645680309 is an equidigital number, since it uses as much as digits as its factorization.

645680309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 155520, while the sum is 41.

The square root of 645680309 is about 25410.2402389273. The cubic root of 645680309 is about 864.3159232233.

The spelling of 645680309 in words is "six hundred forty-five million, six hundred eighty thousand, three hundred nine".