638612166781 has 2 divisors, whose sum is σ = 638612166782. Its totient is φ = 638612166780.

The previous prime is 638612166779. The next prime is 638612166811. The reversal of 638612166781 is 187661216836.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 638226829881 + 385336900 = 798891^2 + 19630^2 .

It is a cyclic number.

It is not a de Polignac number, because 638612166781 - 2¹ = 638612166779 is a prime.

It is a super-2 number, since 2×638612166781² (a number of 24 digits) contains 22 as substring.

Together with 638612166779, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (638612166701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319306083390 + 319306083391.

It is an arithmetic number, because the mean of its divisors is an integer number (319306083391).

Almost surely, 2^638612166781 is an apocalyptic number.

It is an amenable number.

638612166781 is a deficient number, since it is larger than the sum of its proper divisors (1).

638612166781 is an equidigital number, since it uses as much as digits as its factorization.

638612166781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3483648, while the sum is 55.

The spelling of 638612166781 in words is "six hundred thirty-eight billion, six hundred twelve million, one hundred sixty-six thousand, seven hundred eighty-one".