166557421 has 4 divisors (see below), whose sum is σ = 173799072. Its totient is φ = 159315772.

The previous prime is 166557407. The next prime is 166557437. The reversal of 166557421 is 124755661.

It is a happy number.

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.

It is a cyclic number.

It is not a de Polignac number, because 166557421 - 2⁹ = 166556909 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 (166557481) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3620791 + ... + 3620836.

It is an arithmetic number, because the mean of its divisors is an integer number (43449768).

Almost surely, 2^166557421 is an apocalyptic number.

It is an amenable number.

166557421 is a deficient number, since it is larger than the sum of its proper divisors (7241651).

166557421 is an equidigital number, since it uses as much as digits as its factorization.

166557421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7241650.

The product of its digits is 50400, while the sum is 37.

The square root of 166557421 is about 12905.7127273158. The cubic root of 166557421 is about 550.2009414535.

The spelling of 166557421 in words is "one hundred sixty-six million, five hundred fifty-seven thousand, four hundred twenty-one".