161221111 has 4 divisors (see below), whose sum is σ = 166421824. Its totient is φ = 156020400.

The previous prime is 161221103. The next prime is 161221117. The reversal of 161221111 is 111122161.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 111122161 = 2819 ⋅39419.

It is a cyclic number.

It is not a de Polignac number, because 161221111 - 2³ = 161221103 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 (161221117) 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, 2600310 + ... + 2600371.

It is an arithmetic number, because the mean of its divisors is an integer number (41605456).

Almost surely, 2^161221111 is an apocalyptic number.

161221111 is a deficient number, since it is larger than the sum of its proper divisors (5200713).

161221111 is an equidigital number, since it uses as much as digits as its factorization.

161221111 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5200712.

The product of its digits is 24, while the sum is 16.

The square root of 161221111 is about 12697.2875449838. The cubic root of 161221111 is about 544.2611101892.

Adding to 161221111 its reverse (111122161), we get a palindrome (272343272).

The spelling of 161221111 in words is "one hundred sixty-one million, two hundred twenty-one thousand, one hundred eleven".