639974121781 has 2 divisors, whose sum is σ = 639974121782. Its totient is φ = 639974121780.

The previous prime is 639974121769. The next prime is 639974121803. The reversal of 639974121781 is 187121479936.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 523170123025 + 116803998756 = 723305^2 + 341766^2 .

It is a cyclic number.

It is not a de Polignac number, because 639974121781 - 2⁵ = 639974121749 is a prime.

It is a super-2 number, since 2×639974121781² (a number of 24 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (639974121181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319987060890 + 319987060891.

It is an arithmetic number, because the mean of its divisors is an integer number (319987060891).

Almost surely, 2^639974121781 is an apocalyptic number.

It is an amenable number.

639974121781 is a deficient number, since it is larger than the sum of its proper divisors (1).

639974121781 is an equidigital number, since it uses as much as digits as its factorization.

639974121781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4572288, while the sum is 58.

The spelling of 639974121781 in words is "six hundred thirty-nine billion, nine hundred seventy-four million, one hundred twenty-one thousand, seven hundred eighty-one".