645207561 has 24 divisors (see below), whose sum is σ = 955427616. Its totient is φ = 419348160.

The previous prime is 645207509. The next prime is 645207583. The reversal of 645207561 is 165702546.

It is a happy number.

645207561 is a `hidden beast` number, since 6 + 4 + 520 + 75 + 61 = 666.

It is not a de Polignac number, because 645207561 - 2⁹ = 645207049 is a prime.

It is not an unprimeable number, because it can be changed into a prime (645207161) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 263101 + ... + 265541.

It is an arithmetic number, because the mean of its divisors is an integer number (39809484).

Almost surely, 2^645207561 is an apocalyptic number.

It is an amenable number.

645207561 is a deficient number, since it is larger than the sum of its proper divisors (310220055).

645207561 is a wasteful number, since it uses less digits than its factorization.

645207561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3173 (or 3170 counting only the distinct ones).

The product of its (nonzero) digits is 50400, while the sum is 36.

The square root of 645207561 is about 25400.9362229033. The cubic root of 645207561 is about 864.1049295466.

The spelling of 645207561 in words is "six hundred forty-five million, two hundred seven thousand, five hundred sixty-one".