644166661447 has 4 divisors (see below), whose sum is σ = 644248697400. Its totient is φ = 644084625496.

The previous prime is 644166661441. The next prime is 644166661459. The reversal of 644166661447 is 744166661446.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 644166661447 - 2²³ = 644158272839 is a prime.

It is a super-2 number, since 2×644166661447² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644166661441) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 41006197 + ... + 41021902.

It is an arithmetic number, because the mean of its divisors is an integer number (161062174350).

Almost surely, 2^644166661447 is an apocalyptic number.

644166661447 is a deficient number, since it is larger than the sum of its proper divisors (82035953).

644166661447 is an equidigital number, since it uses as much as digits as its factorization.

644166661447 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 82035952.

The product of its digits is 13934592, while the sum is 55.

Subtracting 644166661447 from its reverse (744166661446), we obtain a palindrome (99999999999).

The spelling of 644166661447 in words is "six hundred forty-four billion, one hundred sixty-six million, six hundred sixty-one thousand, four hundred forty-seven".