645623543661 has 4 divisors (see below), whose sum is σ = 860831391552. Its totient is φ = 430415695772.

The previous prime is 645623543651. The next prime is 645623543681. The reversal of 645623543661 is 166345326546.

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 645623543661 - 2⁵ = 645623543629 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645623543611) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 107603923941 + ... + 107603923946.

It is an arithmetic number, because the mean of its divisors is an integer number (215207847888).

Almost surely, 2^645623543661 is an apocalyptic number.

It is an amenable number.

645623543661 is a deficient number, since it is larger than the sum of its proper divisors (215207847891).

645623543661 is a wasteful number, since it uses less digits than its factorization.

645623543661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 215207847890.

The product of its digits is 9331200, while the sum is 51.

The spelling of 645623543661 in words is "six hundred forty-five billion, six hundred twenty-three million, five hundred forty-three thousand, six hundred sixty-one".