638636197561 has 2 divisors, whose sum is σ = 638636197562. Its totient is φ = 638636197560.

The previous prime is 638636197519. The next prime is 638636197627. The reversal of 638636197561 is 165791636836.

It is a happy number.

638636197561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 517162339600 + 121473857961 = 719140^2 + 348531^2 .

It is a cyclic number.

It is not a de Polignac number, because 638636197561 - 2³⁹ = 88880383673 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 638636197561.

It is not a weakly prime, because it can be changed into another prime (638636197501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319318098780 + 319318098781.

It is an arithmetic number, because the mean of its divisors is an integer number (319318098781).

Almost surely, 2^638636197561 is an apocalyptic number.

It is an amenable number.

638636197561 is a deficient number, since it is larger than the sum of its proper divisors (1).

638636197561 is an equidigital number, since it uses as much as digits as its factorization.

638636197561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 29393280, while the sum is 61.

The spelling of 638636197561 in words is "six hundred thirty-eight billion, six hundred thirty-six million, one hundred ninety-seven thousand, five hundred sixty-one".