166666668521 has 4 divisors (see below), whose sum is σ = 166667541072. Its totient is φ = 166665795972.

The previous prime is 166666668479. The next prime is 166666668523. The reversal of 166666668521 is 125866666661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 125866666661 = 479 ⋅262769659.

It is a cyclic number.

It is not a de Polignac number, because 166666668521 - 2¹⁴ = 166666652137 is a prime.

It is a super-4 number, since 4×166666668521⁴ (a number of 46 digits) contains 4444 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (166666668523) 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, 12635 + ... + 577488.

It is an arithmetic number, because the mean of its divisors is an integer number (41666885268).

Almost surely, 2^166666668521 is an apocalyptic number.

It is an amenable number.

166666668521 is a deficient number, since it is larger than the sum of its proper divisors (872551).

166666668521 is an equidigital number, since it uses as much as digits as its factorization.

166666668521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 872550.

The product of its digits is 22394880, while the sum is 59.

The spelling of 166666668521 in words is "one hundred sixty-six billion, six hundred sixty-six million, six hundred sixty-eight thousand, five hundred twenty-one".