643145561 has 4 divisors (see below), whose sum is σ = 663892224. Its totient is φ = 622398900.

The previous prime is 643145551. The next prime is 643145563. The reversal of 643145561 is 165541346.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 165541346 = 2 ⋅82770673.

It is a cyclic number.

It is not a de Polignac number, because 643145561 - 2²⁶ = 576036697 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643145563) 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 3 ways as a sum of consecutive naturals, for example, 10373285 + ... + 10373346.

It is an arithmetic number, because the mean of its divisors is an integer number (165973056).

Almost surely, 2^643145561 is an apocalyptic number.

It is an amenable number.

643145561 is a deficient number, since it is larger than the sum of its proper divisors (20746663).

643145561 is a wasteful number, since it uses less digits than its factorization.

643145561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20746662.

The product of its digits is 43200, while the sum is 35.

The square root of 643145561 is about 25360.3146865334. The cubic root of 643145561 is about 863.1834246091.

The spelling of 643145561 in words is "six hundred forty-three million, one hundred forty-five thousand, five hundred sixty-one".