644278220658 has 54 divisors (see below), whose sum is σ = 1403048057229. Its totient is φ = 213670801872.

The previous prime is 644278220657. The next prime is 644278220681. The reversal of 644278220658 is 856022872446.

644278220658 is a `hidden beast` number, since 6 + 4 + 427 + 8 + 2 + 206 + 5 + 8 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 565478432289 + 78799788369 = 751983^2 + 280713^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=567573.

It is a super-2 number, since 2×644278220658² (a number of 24 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644278220657) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 943305985 + ... + 943306667.

Almost surely, 2^644278220658 is an apocalyptic number.

644278220658 is an abundant number, since it is smaller than the sum of its proper divisors (758769836571).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644278220658 is an frugal number, since it uses more digits than its factorization.

644278220658 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1928 (or 965 counting only the distinct ones).

The product of its (nonzero) digits is 10321920, while the sum is 54.

The spelling of 644278220658 in words is "six hundred forty-four billion, two hundred seventy-eight million, two hundred twenty thousand, six hundred fifty-eight".