165611821 has 8 divisors (see below), whose sum is σ = 167554584. Its totient is φ = 163675200.

The previous prime is 165611819. The next prime is 165611839. The reversal of 165611821 is 128116561.

It can be written as a sum of positive squares in 4 ways, for example, as 139499721 + 26112100 = 11811^2 + 5110^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 165611821 - 2¹ = 165611819 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 (165611521) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 72915 + ... + 75151.

It is an arithmetic number, because the mean of its divisors is an integer number (20944323).

Almost surely, 2^165611821 is an apocalyptic number.

It is an amenable number.

165611821 is a deficient number, since it is larger than the sum of its proper divisors (1942763).

165611821 is a wasteful number, since it uses less digits than its factorization.

165611821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3071.

The product of its digits is 2880, while the sum is 31.

The square root of 165611821 is about 12869.0256429926. The cubic root of 165611821 is about 549.1577422486.

The spelling of 165611821 in words is "one hundred sixty-five million, six hundred eleven thousand, eight hundred twenty-one".