166111511665021 has 4 divisors (see below), whose sum is σ = 178889320254652. Its totient is φ = 153333703075392.

The previous prime is 166111511665013. The next prime is 166111511665049. The reversal of 166111511665021 is 120566115111661.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 103667299977796 + 62444211687225 = 10181714^2 + 7902165^2 .

It is a cyclic number.

It is not a de Polignac number, because 166111511665021 - 2³ = 166111511665013 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (166111511665051) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6388904294796 + ... + 6388904294821.

It is an arithmetic number, because the mean of its divisors is an integer number (44722330063663).

Almost surely, 2^{166111511665021} is an apocalyptic number.

It is an amenable number.

166111511665021 is a deficient number, since it is larger than the sum of its proper divisors (12777808589631).

166111511665021 is a wasteful number, since it uses less digits than its factorization.

166111511665021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12777808589630.

The product of its (nonzero) digits is 64800, while the sum is 43.

Adding to 166111511665021 its reverse (120566115111661), we get a palindrome (286677626776682).

The spelling of 166111511665021 in words is "one hundred sixty-six trillion, one hundred eleven billion, five hundred eleven million, six hundred sixty-five thousand, twenty-one".