643609561 has 12 divisors (see below), whose sum is σ = 768925668. Its totient is φ = 536753952.

The previous prime is 643609543. The next prime is 643609567. The reversal of 643609561 is 165906346.

It can be written as a sum of positive squares in 2 ways, for example, as 302099161 + 341510400 = 17381^2 + 18480^2 .

It is not a de Polignac number, because 643609561 - 2¹³ = 643601369 is a prime.

It is a super-2 number, since 2×643609561² = 828466534021225442, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (643609567) 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 11 ways as a sum of consecutive naturals, for example, 175686 + ... + 179311.

It is an arithmetic number, because the mean of its divisors is an integer number (64077139).

Almost surely, 2^643609561 is an apocalyptic number.

It is an amenable number.

643609561 is a deficient number, since it is larger than the sum of its proper divisors (125316107).

643609561 is a wasteful number, since it uses less digits than its factorization.

643609561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 355048 (or 355041 counting only the distinct ones).

The product of its (nonzero) digits is 116640, while the sum is 40.

The square root of 643609561 is about 25369.4611886023. The cubic root of 643609561 is about 863.3909571147.

The spelling of 643609561 in words is "six hundred forty-three million, six hundred nine thousand, five hundred sixty-one".