166391383921 has 27 divisors (see below), whose sum is σ = 204347349369. Its totient is φ = 135070753608.

The previous prime is 166391383903. The next prime is 166391383943. The reversal of 166391383921 is 129383193661.

The square root of 166391383921 is 407911.

It is a perfect power (a square), and thus also a powerful number.

It is not a de Polignac number, because 166391383921 - 2¹¹ = 166391381873 is a prime.

It is not an unprimeable number, because it can be changed into a prime (166391383121) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 54250630 + ... + 54253696.

It is an arithmetic number, because the mean of its divisors is an integer number (7568420347).

Almost surely, 2^166391383921 is an apocalyptic number.

166391383921 is the 407911-st square number.

166391383921 is the 203956-th centered octagonal number.

It is an amenable number.

166391383921 is a deficient number, since it is larger than the sum of its proper divisors (37955965448).

166391383921 is an frugal number, since it uses more digits than its factorization.

166391383921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6186 (or 3093 counting only the distinct ones).

The product of its digits is 1259712, while the sum is 52.

The spelling of 166391383921 in words is "one hundred sixty-six billion, three hundred ninety-one million, three hundred eighty-three thousand, nine hundred twenty-one".