639128961 has 25 divisors (see below), whose sum is σ = 973108741. Its totient is φ = 418046616.

The previous prime is 639128939. The next prime is 639128977. The reversal of 639128961 is 169821936.

It is a happy number.

The square root of 639128961 is 25281.

It is a perfect power (a square, a biquadrate), and thus also a powerful number.

639128961 is a `hidden beast` number, since 639 + 1 + 2 + 8 + 9 + 6 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 124746561 + 514382400 = 11169^2 + 22680^2 .

It is not a de Polignac number, because 639128961 - 2⁵ = 639128929 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639128981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 24 ways as a sum of consecutive naturals, for example, 12059011 + ... + 12059063.

Almost surely, 2^639128961 is an apocalyptic number.

639128961 is the 25281-st square number.

639128961 is the 12641-st centered octagonal number.

It is an amenable number.

639128961 is a deficient number, since it is larger than the sum of its proper divisors (333979780).

639128961 is an frugal number, since it uses more digits than its factorization.

639128961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 224 (or 56 counting only the distinct ones).

The product of its digits is 139968, while the sum is 45.

The cubic root of 639128961 is about 861.3827408814.

It can be divided in two parts, 639 and 128961, that added together give a square (129600 = 360²).

The spelling of 639128961 in words is "six hundred thirty-nine million, one hundred twenty-eight thousand, nine hundred sixty-one".