643566761 has 4 divisors (see below), whose sum is σ = 646131024. Its totient is φ = 641002500.

The previous prime is 643566751. The next prime is 643566769. The reversal of 643566761 is 167665346.

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.

It is a cyclic number.

It is not a de Polignac number, because 643566761 - 2⁶ = 643566697 is a prime.

It is a super-2 number, since 2×643566761² = 828356351728062242, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643566769) 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 3 ways as a sum of consecutive naturals, for example, 1281755 + ... + 1282256.

It is an arithmetic number, because the mean of its divisors is an integer number (161532756).

Almost surely, 2^643566761 is an apocalyptic number.

It is an amenable number.

643566761 is a deficient number, since it is larger than the sum of its proper divisors (2564263).

643566761 is a wasteful number, since it uses less digits than its factorization.

643566761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2564262.

The product of its digits is 544320, while the sum is 44.

The square root of 643566761 is about 25368.6176406993. The cubic root of 643566761 is about 863.3718182069.

It can be divided in two parts, 64356 and 6761, that added together give a palindrome (71117).

The spelling of 643566761 in words is "six hundred forty-three million, five hundred sixty-six thousand, seven hundred sixty-one".