165818320921 has 4 divisors (see below), whose sum is σ = 180892713744. Its totient is φ = 150743928100.

The previous prime is 165818320919. The next prime is 165818320951. The reversal of 165818320921 is 129023818561.

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: 129023818561 = 11 ⋅11729438051.

It is a cyclic number.

It is not a de Polignac number, because 165818320921 - 2¹ = 165818320919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165818320951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7537196395 + ... + 7537196416.

It is an arithmetic number, because the mean of its divisors is an integer number (45223178436).

Almost surely, 2^165818320921 is an apocalyptic number.

165818320921 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

165818320921 is a deficient number, since it is larger than the sum of its proper divisors (15074392823).

165818320921 is a wasteful number, since it uses less digits than its factorization.

165818320921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15074392822.

The product of its (nonzero) digits is 207360, while the sum is 46.

The spelling of 165818320921 in words is "one hundred sixty-five billion, eight hundred eighteen million, three hundred twenty thousand, nine hundred twenty-one".