639346681 has 2 divisors, whose sum is σ = 639346682. Its totient is φ = 639346680.

The previous prime is 639346657. The next prime is 639346699. The reversal of 639346681 is 186643936.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 557715456 + 81631225 = 23616^2 + 9035^2 .

It is a cyclic number.

It is not a de Polignac number, because 639346681 - 2⁷ = 639346553 is a prime.

It is a super-2 number, since 2×639346681² = 817528357011431522, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (639346601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319673340 + 319673341.

It is an arithmetic number, because the mean of its divisors is an integer number (319673341).

Almost surely, 2^639346681 is an apocalyptic number.

It is an amenable number.

639346681 is a deficient number, since it is larger than the sum of its proper divisors (1).

639346681 is an equidigital number, since it uses as much as digits as its factorization.

639346681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 559872, while the sum is 46.

The square root of 639346681 is about 25285.3056339052. The cubic root of 639346681 is about 861.4805401105.

The spelling of 639346681 in words is "six hundred thirty-nine million, three hundred forty-six thousand, six hundred eighty-one".