639905724981 has 12 divisors (see below), whose sum is σ = 925425944352. Its totient is φ = 426087966696.

The previous prime is 639905724959. The next prime is 639905725001. The reversal of 639905724981 is 189427509936.

639905724981 is a `hidden beast` number, since 6 + 3 + 9 + 90 + 57 + 2 + 498 + 1 = 666.

It is not a de Polignac number, because 639905724981 - 2⁷ = 639905724853 is a prime.

It is a super-2 number, since 2×639905724981² (a number of 24 digits) contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639905704981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 42979641 + ... + 42994526.

It is an arithmetic number, because the mean of its divisors is an integer number (77118828696).

It is a 1-persistent number, because it is pandigital, but 2⋅639905724981 = 1279811449962 is not.

Almost surely, 2^639905724981 is an apocalyptic number.

It is an amenable number.

639905724981 is a deficient number, since it is larger than the sum of its proper divisors (285520219371).

639905724981 is a wasteful number, since it uses less digits than its factorization.

639905724981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 85975000 (or 85974997 counting only the distinct ones).

The product of its (nonzero) digits is 29393280, while the sum is 63.

The spelling of 639905724981 in words is "six hundred thirty-nine billion, nine hundred five million, seven hundred twenty-four thousand, nine hundred eighty-one".