8639625781 has 2 divisors, whose sum is σ = 8639625782. Its totient is φ = 8639625780.

The previous prime is 8639625773. The next prime is 8639625881. The reversal of 8639625781 is 1875269368.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 7725531025 + 914094756 = 87895^2 + 30234^2 .

It is a cyclic number.

It is not a de Polignac number, because 8639625781 - 2³ = 8639625773 is a prime.

It is a super-2 number, since 2×8639625781² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (8639625581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4319812890 + 4319812891.

It is an arithmetic number, because the mean of its divisors is an integer number (4319812891).

Almost surely, 2^8639625781 is an apocalyptic number.

It is an amenable number.

8639625781 is a deficient number, since it is larger than the sum of its proper divisors (1).

8639625781 is an equidigital number, since it uses as much as digits as its factorization.

8639625781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4354560, while the sum is 55.

The square root of 8639625781 is about 92949.5873094658. The cubic root of 8639625781 is about 2051.9415103302.

The spelling of 8639625781 in words is "eight billion, six hundred thirty-nine million, six hundred twenty-five thousand, seven hundred eighty-one".