645697423809 has 27 divisors (see below), whose sum is σ = 948430440867. Its totient is φ = 423311720400.

The previous prime is 645697423801. The next prime is 645697423853. The reversal of 645697423809 is 908324796546.

The square root of 645697423809 is 803553.

It is a perfect power (a square), and thus also a powerful number.

645697423809 is a `hidden beast` number, since 6 + 45 + 6 + 97 + 423 + 80 + 9 = 666.

It can be written as a sum of positive squares in only one way, i.e., 20996879409 + 624700544400 = 144903^2 + 790380^2 .

It is not a de Polignac number, because 645697423809 - 2³ = 645697423801 is a prime.

It is a super-2 number, since 2×645697423809² (a number of 24 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (645697423801) 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 in 26 ways as a sum of consecutive naturals, for example, 147048004 + ... + 147052394.

Almost surely, 2^645697423809 is an apocalyptic number.

645697423809 is the 803553-rd square number.

645697423809 is the 401777-th centered octagonal number.

It is an amenable number.

645697423809 is a deficient number, since it is larger than the sum of its proper divisors (302733017058).

645697423809 is an frugal number, since it uses more digits than its factorization.

645697423809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8910 (or 4455 counting only the distinct ones).

The product of its (nonzero) digits is 78382080, while the sum is 63.

The spelling of 645697423809 in words is "six hundred forty-five billion, six hundred ninety-seven million, four hundred twenty-three thousand, eight hundred nine".