639181681 has 2 divisors, whose sum is σ = 639181682. Its totient is φ = 639181680.

The previous prime is 639181651. The next prime is 639181693. The reversal of 639181681 is 186181936.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 637108081 + 2073600 = 25241^2 + 1440^2 .

It is a cyclic number.

It is not a de Polignac number, because 639181681 - 2⁷ = 639181553 is a prime.

It is a super-2 number, since 2×639181681² = 817106442651971522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (639181651) 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 as a sum of consecutive naturals, namely, 319590840 + 319590841.

It is an arithmetic number, because the mean of its divisors is an integer number (319590841).

Almost surely, 2^639181681 is an apocalyptic number.

It is an amenable number.

639181681 is a deficient number, since it is larger than the sum of its proper divisors (1).

639181681 is an equidigital number, since it uses as much as digits as its factorization.

639181681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 62208, while the sum is 43.

The square root of 639181681 is about 25282.0426587726. The cubic root of 639181681 is about 861.4064245990.

The spelling of 639181681 in words is "six hundred thirty-nine million, one hundred eighty-one thousand, six hundred eighty-one".