165721131 has 6 divisors (see below), whose sum is σ = 239374980. Its totient is φ = 110480748.

The previous prime is 165721099. The next prime is 165721159. The reversal of 165721131 is 131127561.

165721131 is a `hidden beast` number, since 1 + 657 + 2 + 1 + 1 + 3 + 1 = 666.

It is not a de Polignac number, because 165721131 - 2⁵ = 165721099 is a prime.

It is a super-2 number, since 2×165721131² = 54926986519838322, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 165721095 and 165721104.

It is not an unprimeable number, because it can be changed into a prime (165721181) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 9206721 + ... + 9206738.

It is an arithmetic number, because the mean of its divisors is an integer number (39895830).

Almost surely, 2^165721131 is an apocalyptic number.

165721131 is a deficient number, since it is larger than the sum of its proper divisors (73653849).

165721131 is a wasteful number, since it uses less digits than its factorization.

165721131 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18413465 (or 18413462 counting only the distinct ones).

The product of its digits is 1260, while the sum is 27.

The square root of 165721131 is about 12873.2719617042. The cubic root of 165721131 is about 549.2785372303.

Adding to 165721131 its reverse (131127561), we get a palindrome (296848692).

The spelling of 165721131 in words is "one hundred sixty-five million, seven hundred twenty-one thousand, one hundred thirty-one".