161664221 has 4 divisors (see below), whose sum is σ = 162039744. Its totient is φ = 161288700.

The previous prime is 161664197. The next prime is 161664227. The reversal of 161664221 is 122466161.

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 an emirpimes, since its reverse is a distinct semiprime: 122466161 = 47 ⋅2605663.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-161664221 is a prime.

It is a super-2 number, since 2×161664221² = 52270640703073682, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161664227) 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, 187115 + ... + 187976.

It is an arithmetic number, because the mean of its divisors is an integer number (40509936).

Almost surely, 2^161664221 is an apocalyptic number.

It is an amenable number.

161664221 is a deficient number, since it is larger than the sum of its proper divisors (375523).

161664221 is an equidigital number, since it uses as much as digits as its factorization.

161664221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 375522.

The product of its digits is 3456, while the sum is 29.

The square root of 161664221 is about 12714.7245742879. The cubic root of 161664221 is about 544.7592809503.

The spelling of 161664221 in words is "one hundred sixty-one million, six hundred sixty-four thousand, two hundred twenty-one".