639974121805 has 8 divisors (see below), whose sum is σ = 767995972632. Its totient is φ = 511961279808.

The previous prime is 639974121803. The next prime is 639974121953. The reversal of 639974121805 is 508121479936.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 124032161124 + 515941960681 = 352182^2 + 718291^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 639974121805 - 2¹ = 639974121803 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639974121803) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2094922 + ... + 2380891.

It is an arithmetic number, because the mean of its divisors is an integer number (95999496579).

It is a 1-persistent number, because it is pandigital, but 2⋅639974121805 = 1279948243610 is not.

Almost surely, 2^639974121805 is an apocalyptic number.

It is an amenable number.

639974121805 is a deficient number, since it is larger than the sum of its proper divisors (128021850827).

639974121805 is a wasteful number, since it uses less digits than its factorization.

639974121805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4504415.

The product of its (nonzero) digits is 3265920, while the sum is 55.

The spelling of 639974121805 in words is "six hundred thirty-nine billion, nine hundred seventy-four million, one hundred twenty-one thousand, eight hundred five".