644641761761 has 8 divisors (see below), whose sum is σ = 683823542184. Its totient is φ = 605600167680.

The previous prime is 644641761739. The next prime is 644641761767. The reversal of 644641761761 is 167167146446.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 30714665536 + 613927096225 = 175256^2 + 783535^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644641761761 is a prime.

It is a super-2 number, since 2×644641761761² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (644641761767) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 35037110 + ... + 35055503.

It is an arithmetic number, because the mean of its divisors is an integer number (85477942773).

Almost surely, 2^644641761761 is an apocalyptic number.

It is an amenable number.

644641761761 is a deficient number, since it is larger than the sum of its proper divisors (39181780423).

644641761761 is a wasteful number, since it uses less digits than its factorization.

644641761761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 70093171.

The product of its digits is 4064256, while the sum is 53.

The spelling of 644641761761 in words is "six hundred forty-four billion, six hundred forty-one million, seven hundred sixty-one thousand, seven hundred sixty-one".