639721569 has 4 divisors (see below), whose sum is σ = 852962096. Its totient is φ = 426481044.

The previous prime is 639721553. The next prime is 639721591. The reversal of 639721569 is 965127936.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 639721569 - 2⁴ = 639721553 is a prime.

It is a super-2 number, since 2×639721569² = 818487371687643522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639721529) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106620259 + ... + 106620264.

It is an arithmetic number, because the mean of its divisors is an integer number (213240524).

Almost surely, 2^639721569 is an apocalyptic number.

It is an amenable number.

639721569 is a deficient number, since it is larger than the sum of its proper divisors (213240527).

639721569 is a wasteful number, since it uses less digits than its factorization.

639721569 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213240526.

The product of its digits is 612360, while the sum is 48.

The square root of 639721569 is about 25292.7177068816. The cubic root of 639721569 is about 861.6488867595.

It can be divided in two parts, 6397 and 21569, that added together give a triangular number (27966 = T₂₃₆).

The spelling of 639721569 in words is "six hundred thirty-nine million, seven hundred twenty-one thousand, five hundred sixty-nine".