638723709 has 12 divisors (see below), whose sum is σ = 993570396. Its totient is φ = 393060672.

The previous prime is 638723699. The next prime is 638723717. The reversal of 638723709 is 907327836.

It is a happy number.

638723709 is a `hidden beast` number, since 638 + 7 + 2 + 3 + 7 + 0 + 9 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 209612484 + 429111225 = 14478^2 + 20715^2 .

It is not a de Polignac number, because 638723709 - 2⁴ = 638723693 is a prime.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638723509) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2729472 + ... + 2729705.

It is an arithmetic number, because the mean of its divisors is an integer number (82797533).

Almost surely, 2^638723709 is an apocalyptic number.

It is an amenable number.

638723709 is a deficient number, since it is larger than the sum of its proper divisors (354846687).

638723709 is a wasteful number, since it uses less digits than its factorization.

638723709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5459196 (or 5459193 counting only the distinct ones).

The product of its (nonzero) digits is 381024, while the sum is 45.

The square root of 638723709 is about 25272.9837771483. The cubic root of 638723709 is about 861.2006436284.

The spelling of 638723709 in words is "six hundred thirty-eight million, seven hundred twenty-three thousand, seven hundred nine".