639740768409261 has 24 divisors (see below), whose sum is σ = 931158630675000. Its totient is φ = 423227626716672.

The previous prime is 639740768409257. The next prime is 639740768409269. The reversal of 639740768409261 is 162904867047936.

It is a happy number.

639740768409261 is a `hidden beast` number, since 6 + 3 + 97 + 4 + 0 + 76 + 8 + 409 + 2 + 61 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 251324901432900 + 388415866976361 = 15853230^2 + 19708269^2 .

It is not a de Polignac number, because 639740768409261 - 2² = 639740768409257 is a prime.

It is a super-2 number, since 2×639740768409261² (a number of 30 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 639740768409261.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639740768409269) 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, 225982456 + ... + 228795873.

It is an arithmetic number, because the mean of its divisors is an integer number (38798276278125).

Almost surely, 2^{639740768409261} is an apocalyptic number.

It is an amenable number.

639740768409261 is a deficient number, since it is larger than the sum of its proper divisors (291417862265739).

639740768409261 is a wasteful number, since it uses less digits than its factorization.

639740768409261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 454779533 (or 454779530 counting only the distinct ones).

The product of its (nonzero) digits is 658409472, while the sum is 72.

The spelling of 639740768409261 in words is "six hundred thirty-nine trillion, seven hundred forty billion, seven hundred sixty-eight million, four hundred nine thousand, two hundred sixty-one".