165521231 has 4 divisors (see below), whose sum is σ = 175257792. Its totient is φ = 155784672.

The previous prime is 165521207. The next prime is 165521249. The reversal of 165521231 is 132125561.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 132125561 = 5273 ⋅25057.

It is a cyclic number.

It is not a de Polignac number, because 165521231 - 2²⁶ = 98412367 is a prime.

It is a super-2 number, since 2×165521231² = 54794555823510722, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 165521231.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (165521261) 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, 4868255 + ... + 4868288.

It is an arithmetic number, because the mean of its divisors is an integer number (43814448).

Almost surely, 2^165521231 is an apocalyptic number.

165521231 is a deficient number, since it is larger than the sum of its proper divisors (9736561).

165521231 is an equidigital number, since it uses as much as digits as its factorization.

165521231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9736560.

The product of its digits is 1800, while the sum is 26.

The square root of 165521231 is about 12865.5054700544. The cubic root of 165521231 is about 549.0575938552.

Adding to 165521231 its reverse (132125561), we get a palindrome (297646792).

The spelling of 165521231 in words is "one hundred sixty-five million, five hundred twenty-one thousand, two hundred thirty-one".