645664689 has 40 divisors (see below), whose sum is σ = 1001242088. Its totient is φ = 414305280.

The previous prime is 645664609. The next prime is 645664751. The reversal of 645664689 is 986466546.

It can be written as a sum of positive squares in 4 ways, for example, as 258952464 + 386712225 = 16092^2 + 19665^2 .

It is not a de Polignac number, because 645664689 - 2⁷ = 645664561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (645664609) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 289599 + ... + 291819.

Almost surely, 2^645664689 is an apocalyptic number.

It is an amenable number.

645664689 is a deficient number, since it is larger than the sum of its proper divisors (355577399).

645664689 is a wasteful number, since it uses less digits than its factorization.

645664689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2367 (or 2358 counting only the distinct ones).

The product of its digits is 7464960, while the sum is 54.

The square root of 645664689 is about 25409.9328806670. The cubic root of 645664689 is about 864.3089534565.

The spelling of 645664689 in words is "six hundred forty-five million, six hundred sixty-four thousand, six hundred eighty-nine".