638721787 has 32 divisors (see below), whose sum is σ = 740471040. Its totient is φ = 545719680.

The previous prime is 638721779. The next prime is 638721791. The reversal of 638721787 is 787127836.

It is not a de Polignac number, because 638721787 - 2³ = 638721779 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 638721787.

It is not an unprimeable number, because it can be changed into a prime (638721757) 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, 1608673 + ... + 1609069.

It is an arithmetic number, because the mean of its divisors is an integer number (23139720).

Almost surely, 2^638721787 is an apocalyptic number.

638721787 is a gapful number since it is divisible by the number (67) formed by its first and last digit.

638721787 is a deficient number, since it is larger than the sum of its proper divisors (101749253).

638721787 is a wasteful number, since it uses less digits than its factorization.

638721787 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 571.

The product of its digits is 790272, while the sum is 49.

The square root of 638721787 is about 25272.9457523257. The cubic root of 638721787 is about 861.1997798072.

The spelling of 638721787 in words is "six hundred thirty-eight million, seven hundred twenty-one thousand, seven hundred eighty-seven".