21766565081 has 2 divisors, whose sum is σ = 21766565082. Its totient is φ = 21766565080.

The previous prime is 21766565057. The next prime is 21766565087. The reversal of 21766565081 is 18056566712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21702003856 + 64561225 = 147316^2 + 8035^2 .

It is a cyclic number.

It is not a de Polignac number, because 21766565081 - 2¹⁴ = 21766548697 is a prime.

It is a super-2 number, since 2×21766565081² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21766565087) 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, 10883282540 + 10883282541.

It is an arithmetic number, because the mean of its divisors is an integer number (10883282541).

Almost surely, 2^21766565081 is an apocalyptic number.

It is an amenable number.

21766565081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21766565081 is an equidigital number, since it uses as much as digits as its factorization.

21766565081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 604800, while the sum is 47.

The spelling of 21766565081 in words is "twenty-one billion, seven hundred sixty-six million, five hundred sixty-five thousand, eighty-one".