639745625281 has 27 divisors (see below), whose sum is σ = 749857201443. Its totient is φ = 544211816400.

The previous prime is 639745625203. The next prime is 639745625291. The reversal of 639745625281 is 182526547936.

The square root of 639745625281 is 799841.

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

It can be written as a sum of positive squares in only one way, i.e., 551738469681 + 88007155600 = 742791^2 + 296660^2 .

It is not a de Polignac number, because 639745625281 - 2²¹ = 639743528129 is a prime.

It is a super-2 number, since 2×639745625281² (a number of 24 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (639745625291) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 912618231 + ... + 912618931.

Almost surely, 2^639745625281 is an apocalyptic number.

639745625281 is the 799841-st square number.

639745625281 is the 399921-st centered octagonal number.

It is an amenable number.

639745625281 is a deficient number, since it is larger than the sum of its proper divisors (110111576162).

639745625281 is an frugal number, since it uses more digits than its factorization.

639745625281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1742 (or 871 counting only the distinct ones).

The product of its digits is 21772800, while the sum is 58.

The spelling of 639745625281 in words is "six hundred thirty-nine billion, seven hundred forty-five million, six hundred twenty-five thousand, two hundred eighty-one".