8681566781 has 2 divisors, whose sum is σ = 8681566782. Its totient is φ = 8681566780.

The previous prime is 8681566757. The next prime is 8681566793. The reversal of 8681566781 is 1876651868.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 5887492900 + 2794073881 = 76730^2 + 52859^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-8681566781 is a prime.

It is a super-2 number, since 2×8681566781² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (8681506781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4340783390 + 4340783391.

It is an arithmetic number, because the mean of its divisors is an integer number (4340783391).

Almost surely, 2^8681566781 is an apocalyptic number.

It is an amenable number.

8681566781 is a deficient number, since it is larger than the sum of its proper divisors (1).

8681566781 is an equidigital number, since it uses as much as digits as its factorization.

8681566781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3870720, while the sum is 56.

The square root of 8681566781 is about 93174.9257096565. The cubic root of 8681566781 is about 2055.2565301949.

The spelling of 8681566781 in words is "eight billion, six hundred eighty-one million, five hundred sixty-six thousand, seven hundred eighty-one".