165835721 has 4 divisors (see below), whose sum is σ = 166210512. Its totient is φ = 165460932.

The previous prime is 165835699. The next prime is 165835729. The reversal of 165835721 is 127538561.

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: 127538561 = 691 ⋅184571.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-165835721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165835729) 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, 186731 + ... + 187616.

It is an arithmetic number, because the mean of its divisors is an integer number (41552628).

Almost surely, 2^165835721 is an apocalyptic number.

It is an amenable number.

165835721 is a deficient number, since it is larger than the sum of its proper divisors (374791).

165835721 is an equidigital number, since it uses as much as digits as its factorization.

165835721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 374790.

The product of its digits is 50400, while the sum is 38.

The square root of 165835721 is about 12877.7218870420. The cubic root of 165835721 is about 549.4051099561.

The spelling of 165835721 in words is "one hundred sixty-five million, eight hundred thirty-five thousand, seven hundred twenty-one".