644139486 has 64 divisors (see below), whose sum is σ = 1519594560. Its totient is φ = 201553920.

The previous prime is 644139481. The next prime is 644139487. The reversal of 644139486 is 684931446.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644139481) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 495990 + ... + 497286.

It is an arithmetic number, because the mean of its divisors is an integer number (23743665).

Almost surely, 2^644139486 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644139486, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (759797280).

644139486 is an abundant number, since it is smaller than the sum of its proper divisors (875455074).

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

644139486 is a wasteful number, since it uses less digits than its factorization.

644139486 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1866 (or 1860 counting only the distinct ones).

The product of its digits is 497664, while the sum is 45.

The square root of 644139486 is about 25379.9031913047. The cubic root of 644139486 is about 863.6278538122.

The spelling of 644139486 in words is "six hundred forty-four million, one hundred thirty-nine thousand, four hundred eighty-six".