165623721 has 4 divisors (see below), whose sum is σ = 220831632. Its totient is φ = 110415812.

The previous prime is 165623701. The next prime is 165623747. The reversal of 165623721 is 127326561.

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: 127326561 = 3 ⋅42442187.

It is a cyclic number.

It is not a de Polignac number, because 165623721 - 2⁶ = 165623657 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (165623701) 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, 27603951 + ... + 27603956.

It is an arithmetic number, because the mean of its divisors is an integer number (55207908).

Almost surely, 2^165623721 is an apocalyptic number.

It is an amenable number.

165623721 is a deficient number, since it is larger than the sum of its proper divisors (55207911).

165623721 is an equidigital number, since it uses as much as digits as its factorization.

165623721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55207910.

The product of its digits is 15120, while the sum is 33.

The square root of 165623721 is about 12869.4879851531. The cubic root of 165623721 is about 549.1708951354.

The spelling of 165623721 in words is "one hundred sixty-five million, six hundred twenty-three thousand, seven hundred twenty-one".