644121108 has 18 divisors (see below), whose sum is σ = 1628195114. Its totient is φ = 214707024.

The previous prime is 644121097. The next prime is 644121133. The reversal of 644121108 is 801121446.

It is a happy number.

644121108 is a `hidden beast` number, since 6 + 441 + 211 + 0 + 8 = 666.

It can be written as a sum of positive squares in only one way, i.e., 638977284 + 5143824 = 25278^2 + 2268^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a super-2 number, since 2×644121108² = 829784003542295328, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8946091 + ... + 8946162.

Almost surely, 2^644121108 is an apocalyptic number.

It is an amenable number.

644121108 is an abundant number, since it is smaller than the sum of its proper divisors (984074006).

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

644121108 is a wasteful number, since it uses less digits than its factorization.

644121108 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17892263 (or 17892258 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 27.

The square root of 644121108 is about 25379.5411306036. The cubic root of 644121108 is about 863.6196403202.

The spelling of 644121108 in words is "six hundred forty-four million, one hundred twenty-one thousand, one hundred eight".