165720121 has 8 divisors (see below), whose sum is σ = 189552960. Its totient is φ = 141926928.

The previous prime is 165720101. The next prime is 165720133. The reversal of 165720121 is 121027561.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 165720121 - 2⁷ = 165719993 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165720101) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 331 + ... + 18208.

It is an arithmetic number, because the mean of its divisors is an integer number (23694120).

Almost surely, 2^165720121 is an apocalyptic number.

It is an amenable number.

165720121 is a deficient number, since it is larger than the sum of its proper divisors (23832839).

165720121 is a wasteful number, since it uses less digits than its factorization.

165720121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19823.

The product of its (nonzero) digits is 840, while the sum is 25.

The square root of 165720121 is about 12873.2327330784. The cubic root of 165720121 is about 549.2774213548.

Adding to 165720121 its reverse (121027561), we get a palindrome (286747682).

The spelling of 165720121 in words is "one hundred sixty-five million, seven hundred twenty thousand, one hundred twenty-one".