165040021 has 4 divisors (see below), whose sum is σ = 165530092. Its totient is φ = 164549952.

The previous prime is 165039991. The next prime is 165040049. The reversal of 165040021 is 120040561.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 27447121 + 137592900 = 5239^2 + 11730^2 .

It is a cyclic number.

It is not a de Polignac number, because 165040021 - 2¹³ = 165031829 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 (165040721) 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, 244530 + ... + 245203.

It is an arithmetic number, because the mean of its divisors is an integer number (41382523).

Almost surely, 2^165040021 is an apocalyptic number.

It is an amenable number.

165040021 is a deficient number, since it is larger than the sum of its proper divisors (490071).

165040021 is an equidigital number, since it uses as much as digits as its factorization.

165040021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 490070.

The product of its (nonzero) digits is 240, while the sum is 19.

The square root of 165040021 is about 12846.7902995262. The cubic root of 165040021 is about 548.5249965964.

Adding to 165040021 its reverse (120040561), we get a palindrome (285080582).

The spelling of 165040021 in words is "one hundred sixty-five million, forty thousand, twenty-one".