644981904 has 360 divisors, whose sum is σ = 2348555040. Its totient is φ = 163731456.

The previous prime is 644981881. The next prime is 644981917. The reversal of 644981904 is 409189446.

644981904 = T₂ + T₃ + ... + T₁₅₆₉.

It is a self number, because there is not a number n which added to its sum of digits gives 644981904.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 2278947 + ... + 2279229.

It is an arithmetic number, because the mean of its divisors is an integer number (6523764).

Almost surely, 2^644981904 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644981904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1174277520).

644981904 is an abundant number, since it is smaller than the sum of its proper divisors (1703573136).

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

644981904 is a wasteful number, since it uses less digits than its factorization.

644981904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 347 (or 331 counting only the distinct ones).

The product of its (nonzero) digits is 248832, while the sum is 45.

The square root of 644981904 is about 25396.4939312496. The cubic root of 644981904 is about 864.0041795065.

The spelling of 644981904 in words is "six hundred forty-four million, nine hundred eighty-one thousand, nine hundred four".