161756221 has 4 divisors (see below), whose sum is σ = 176461344. Its totient is φ = 147051100.

The previous prime is 161756167. The next prime is 161756227. The reversal of 161756221 is 122657161.

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: 122657161 = 11 ⋅11150651.

It is a cyclic number.

It is not a de Polignac number, because 161756221 - 2¹⁹ = 161231933 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 (161756227) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7352545 + ... + 7352566.

It is an arithmetic number, because the mean of its divisors is an integer number (44115336).

Almost surely, 2^161756221 is an apocalyptic number.

161756221 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

161756221 is a deficient number, since it is larger than the sum of its proper divisors (14705123).

161756221 is a wasteful number, since it uses less digits than its factorization.

161756221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14705122.

The product of its digits is 5040, while the sum is 31.

The square root of 161756221 is about 12718.3419123721. The cubic root of 161756221 is about 544.8625986985.

The spelling of 161756221 in words is "one hundred sixty-one million, seven hundred fifty-six thousand, two hundred twenty-one".