639561969 has 24 divisors (see below), whose sum is σ = 964477800. Its totient is φ = 407877120.

The previous prime is 639561953. The next prime is 639561991. The reversal of 639561969 is 969165936.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 28483569 + 611078400 = 5337^2 + 24720^2 .

It is not a de Polignac number, because 639561969 - 2⁴ = 639561953 is a prime.

It is a super-2 number, since 2×639561969² = 818079024382313922, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (639561929) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 17209 + ... + 39689.

It is an arithmetic number, because the mean of its divisors is an integer number (40186575).

Almost surely, 2^639561969 is an apocalyptic number.

It is an amenable number.

639561969 is a deficient number, since it is larger than the sum of its proper divisors (324915831).

639561969 is a wasteful number, since it uses less digits than its factorization.

639561969 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22625 (or 22622 counting only the distinct ones).

The product of its digits is 2361960, while the sum is 54.

The square root of 639561969 is about 25289.5624517310. The cubic root of 639561969 is about 861.5772250622.

The spelling of 639561969 in words is "six hundred thirty-nine million, five hundred sixty-one thousand, nine hundred sixty-nine".