638865666505 has 16 divisors (see below), whose sum is σ = 836918596800. Its totient is φ = 464304375360.

The previous prime is 638865666503. The next prime is 638865666511. The reversal of 638865666505 is 505666568836.

It is a happy number.

It is not a de Polignac number, because 638865666505 - 2¹ = 638865666503 is a prime.

It is not an unprimeable number, because it can be changed into a prime (638865666503) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3985695 + ... + 4142884.

It is an arithmetic number, because the mean of its divisors is an integer number (52307412300).

Almost surely, 2^638865666505 is an apocalyptic number.

It is an amenable number.

638865666505 is a deficient number, since it is larger than the sum of its proper divisors (198052930295).

638865666505 is a wasteful number, since it uses less digits than its factorization.

638865666505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8130024.

The product of its (nonzero) digits is 186624000, while the sum is 64.

The spelling of 638865666505 in words is "six hundred thirty-eight billion, eight hundred sixty-five million, six hundred sixty-six thousand, five hundred five".