165745721 has 4 divisors (see below), whose sum is σ = 174469200. Its totient is φ = 157022244.

The previous prime is 165745711. The next prime is 165745729. The reversal of 165745721 is 127547561.

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: 127547561 = 491 ⋅259771.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-165745721 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (165745729) 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, 4361711 + ... + 4361748.

It is an arithmetic number, because the mean of its divisors is an integer number (43617300).

Almost surely, 2^165745721 is an apocalyptic number.

It is an amenable number.

165745721 is a deficient number, since it is larger than the sum of its proper divisors (8723479).

165745721 is an equidigital number, since it uses as much as digits as its factorization.

165745721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8723478.

The product of its digits is 58800, while the sum is 38.

The square root of 165745721 is about 12874.2270059216. The cubic root of 165745721 is about 549.3057035330.

The spelling of 165745721 in words is "one hundred sixty-five million, seven hundred forty-five thousand, seven hundred twenty-one".