166905621 has 6 divisors (see below), whose sum is σ = 241085910. Its totient is φ = 111270408.

The previous prime is 166905617. The next prime is 166905637. The reversal of 166905621 is 126509661.

166905621 is a `hidden beast` number, since 1 + 6 + 6 + 90 + 562 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 161569521 + 5336100 = 12711^2 + 2310^2 .

It is not a de Polignac number, because 166905621 - 2² = 166905617 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (166905611) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 9272526 + ... + 9272543.

It is an arithmetic number, because the mean of its divisors is an integer number (40180985).

Almost surely, 2^166905621 is an apocalyptic number.

It is an amenable number.

166905621 is a deficient number, since it is larger than the sum of its proper divisors (74180289).

166905621 is a wasteful number, since it uses less digits than its factorization.

166905621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18545075 (or 18545072 counting only the distinct ones).

The product of its (nonzero) digits is 19440, while the sum is 36.

The square root of 166905621 is about 12919.1958341067. The cubic root of 166905621 is about 550.5840858324.

Subtracting from 166905621 its sum of digits (36), we obtain a triangular number (166905585 = T₁₈₂₇₀).

The spelling of 166905621 in words is "one hundred sixty-six million, nine hundred five thousand, six hundred twenty-one".