166540021 has 4 divisors (see below), whose sum is σ = 167267500. Its totient is φ = 165812544.

The previous prime is 166540019. The next prime is 166540037. The reversal of 166540021 is 120045661.

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 97732996 + 68807025 = 9886^2 + 8295^2 .

It is a cyclic number.

It is not a de Polignac number, because 166540021 - 2¹ = 166540019 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 (166540001) 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 in 3 ways as a sum of consecutive naturals, for example, 363396 + ... + 363853.

It is an arithmetic number, because the mean of its divisors is an integer number (41816875).

Almost surely, 2^166540021 is an apocalyptic number.

It is an amenable number.

166540021 is a deficient number, since it is larger than the sum of its proper divisors (727479).

166540021 is an equidigital number, since it uses as much as digits as its factorization.

166540021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 727478.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 166540021 is about 12905.0385896362. The cubic root of 166540021 is about 550.1817812349.

Adding to 166540021 its reverse (120045661), we get a palindrome (286585682).

The spelling of 166540021 in words is "one hundred sixty-six million, five hundred forty thousand, twenty-one".