7821166781 has 2 divisors, whose sum is σ = 7821166782. Its totient is φ = 7821166780.

The previous prime is 7821166697. The next prime is 7821166841. The reversal of 7821166781 is 1876611287.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 7819864900 + 1301881 = 88430^2 + 1141^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-7821166781 is a prime.

It is a super-2 number, since 2×7821166781² (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 (7821166181) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3910583390 + 3910583391.

It is an arithmetic number, because the mean of its divisors is an integer number (3910583391).

Almost surely, 2^7821166781 is an apocalyptic number.

It is an amenable number.

7821166781 is a deficient number, since it is larger than the sum of its proper divisors (1).

7821166781 is an equidigital number, since it uses as much as digits as its factorization.

7821166781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 225792, while the sum is 47.

The square root of 7821166781 is about 88437.3607758621. The cubic root of 7821166781 is about 1984.9847855238.

The spelling of 7821166781 in words is "seven billion, eight hundred twenty-one million, one hundred sixty-six thousand, seven hundred eighty-one".