28721 has 8 divisors (see below), whose sum is σ = 35904. Its totient is φ = 22320.

The previous prime is 28711. The next prime is 28723. The reversal of 28721 is 12782.

28721 = 46² + 47² + ... + 56².

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 28721 - 2⁶ = 28657 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 28693 and 28702.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 28721.

It is not an unprimeable number, because it can be changed into a prime (28723) 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, 110 + ... + 263.

It is an arithmetic number, because the mean of its divisors is an integer number (4488).

2²⁸⁷²¹ is an apocalyptic number.

It is an amenable number.

28721 is a deficient number, since it is larger than the sum of its proper divisors (7183).

28721 is a wasteful number, since it uses less digits than its factorization.

28721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 391.

The product of its digits is 224, while the sum is 20.

The square root of 28721 is about 169.4727116677. The cubic root of 28721 is about 30.6243245721.

The spelling of 28721 in words is "twenty-eight thousand, seven hundred twenty-one".