639723761 has 4 divisors (see below), whose sum is σ = 639793524. Its totient is φ = 639654000.

The previous prime is 639723739. The next prime is 639723767. The reversal of 639723761 is 167327936.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 122434225 + 517289536 = 11065^2 + 22744^2 .

It is a cyclic number.

It is not a de Polignac number, because 639723761 - 2¹⁴ = 639707377 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639723767) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18590 + ... + 40311.

It is an arithmetic number, because the mean of its divisors is an integer number (159948381).

Almost surely, 2^639723761 is an apocalyptic number.

It is an amenable number.

639723761 is a deficient number, since it is larger than the sum of its proper divisors (69763).

639723761 is a wasteful number, since it uses less digits than its factorization.

639723761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69762.

The product of its digits is 285768, while the sum is 44.

The square root of 639723761 is about 25292.7610394753. The cubic root of 639723761 is about 861.6498709023.

The spelling of 639723761 in words is "six hundred thirty-nine million, seven hundred twenty-three thousand, seven hundred sixty-one".