128721 has 8 divisors (see below), whose sum is σ = 173664. Its totient is φ = 84800.

The previous prime is 128717. The next prime is 128747. The reversal of 128721 is 127821.

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 128721 - 2² = 128717 is a prime.

It is a Curzon number.

128721 is a lucky number.

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (128761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 121 + ... + 521.

It is an arithmetic number, because the mean of its divisors is an integer number (21708).

2¹²⁸⁷²¹ is an apocalyptic number.

It is an amenable number.

128721 is a deficient number, since it is larger than the sum of its proper divisors (44943).

128721 is a wasteful number, since it uses less digits than its factorization.

128721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 511.

The product of its digits is 224, while the sum is 21.

The square root of 128721 is about 358.7770895696. Note that the first 3 decimals coincide. The cubic root of 128721 is about 50.4912902013.

Subtracting from 128721 its reverse (127821), we obtain a square (900 = 30²).

The spelling of 128721 in words is "one hundred twenty-eight thousand, seven hundred twenty-one".