165721540 has 24 divisors (see below), whose sum is σ = 348949440. Its totient is φ = 66110688.

The previous prime is 165721531. The next prime is 165721547. The reversal of 165721540 is 45127561.

It is not an unprimeable number, because it can be changed into a prime (165721547) 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 7 ways as a sum of consecutive naturals, for example, 3352 + ... + 18511.

It is an arithmetic number, because the mean of its divisors is an integer number (14539560).

Almost surely, 2^165721540 is an apocalyptic number.

165721540 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

165721540 is an abundant number, since it is smaller than the sum of its proper divisors (183227900).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

165721540 is a wasteful number, since it uses less digits than its factorization.

165721540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22251 (or 22249 counting only the distinct ones).

The product of its (nonzero) digits is 8400, while the sum is 31.

The square root of 165721540 is about 12873.2878473217. The cubic root of 165721540 is about 549.2789891033.

The spelling of 165721540 in words is "one hundred sixty-five million, seven hundred twenty-one thousand, five hundred forty".