638721720 has 512 divisors, whose sum is σ = 2686924800. Its totient is φ = 131383296.

The previous prime is 638721701. The next prime is 638721757. The reversal of 638721720 is 27127836.

638721720 is a `hidden beast` number, since 638 + 7 + 2 + 17 + 2 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 6584712 + ... + 6584808.

It is an arithmetic number, because the mean of its divisors is an integer number (5247900).

Almost surely, 2^638721720 is an apocalyptic number.

638721720 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 638721720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1343462400).

638721720 is an abundant number, since it is smaller than the sum of its proper divisors (2048203080).

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

638721720 is a wasteful number, since it uses less digits than its factorization.

638721720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 204 (or 194 counting only the distinct ones).

The product of its (nonzero) digits is 28224, while the sum is 36.

The square root of 638721720 is about 25272.9444267976. The cubic root of 638721720 is about 861.1997496948.

The spelling of 638721720 in words is "six hundred thirty-eight million, seven hundred twenty-one thousand, seven hundred twenty".