165005721 has 16 divisors (see below), whose sum is σ = 245529600. Its totient is φ = 109519344.

The previous prime is 165005719. The next prime is 165005741. The reversal of 165005721 is 127500561.

165005721 is a `hidden beast` number, since 1 + 650 + 0 + 5 + 7 + 2 + 1 = 666.

It is not a de Polignac number, because 165005721 - 2¹ = 165005719 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (165005741) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7161 + ... + 19526.

It is an arithmetic number, because the mean of its divisors is an integer number (15345600).

Almost surely, 2^165005721 is an apocalyptic number.

It is an amenable number.

165005721 is a deficient number, since it is larger than the sum of its proper divisors (80523879).

165005721 is a wasteful number, since it uses less digits than its factorization.

165005721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26925 (or 26919 counting only the distinct ones).

The product of its (nonzero) digits is 2100, while the sum is 27.

The square root of 165005721 is about 12845.4552663578. The cubic root of 165005721 is about 548.4869942767.

The spelling of 165005721 in words is "one hundred sixty-five million, five thousand, seven hundred twenty-one".