81166106261 has 2 divisors, whose sum is σ = 81166106262. Its totient is φ = 81166106260.

The previous prime is 81166106249. The next prime is 81166106269. The reversal of 81166106261 is 16260166118.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 75616750225 + 5549356036 = 274985^2 + 74494^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81166106261 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81166106269) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40583053130 + 40583053131.

It is an arithmetic number, because the mean of its divisors is an integer number (40583053131).

Almost surely, 2^81166106261 is an apocalyptic number.

It is an amenable number.

81166106261 is a deficient number, since it is larger than the sum of its proper divisors (1).

81166106261 is an equidigital number, since it uses as much as digits as its factorization.

81166106261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 20736, while the sum is 38.

The spelling of 81166106261 in words is "eighty-one billion, one hundred sixty-six million, one hundred six thousand, two hundred sixty-one".