639171918 has 128 divisors (see below), whose sum is σ = 1779978240. Its totient is φ = 165166560.

The previous prime is 639171889. The next prime is 639171931. The reversal of 639171918 is 819171936.

639171918 is a `hidden beast` number, since 639 + 1 + 7 + 1 + 9 + 1 + 8 = 666.

It is a Smith number, since the sum of its digits (45) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 1442605 + ... + 1443047.

It is an arithmetic number, because the mean of its divisors is an integer number (13906080).

Almost surely, 2^639171918 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 639171918, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (889989120).

639171918 is an abundant number, since it is smaller than the sum of its proper divisors (1140806322).

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

639171918 is a wasteful number, since it uses less digits than its factorization.

639171918 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 819 (or 813 counting only the distinct ones).

The product of its digits is 81648, while the sum is 45.

The square root of 639171918 is about 25281.8495763265. The cubic root of 639171918 is about 861.4020388070.

The spelling of 639171918 in words is "six hundred thirty-nine million, one hundred seventy-one thousand, nine hundred eighteen".