28130721 has 8 divisors (see below), whose sum is σ = 37565280. Its totient is φ = 18724992.

The previous prime is 28130719. The next prime is 28130737. The reversal of 28130721 is 12703182.

28130721 is nontrivially palindromic in base 16.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 28130721 - 2¹ = 28130719 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 28130691 and 28130700.

It is not an unprimeable number, because it can be changed into a prime (28130701) 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, 4816 + ... + 8913.

It is an arithmetic number, because the mean of its divisors is an integer number (4695660).

Almost surely, 2^28130721 is an apocalyptic number.

It is an amenable number.

28130721 is a deficient number, since it is larger than the sum of its proper divisors (9434559).

28130721 is a wasteful number, since it uses less digits than its factorization.

28130721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14415.

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 28130721 is about 5303.8402125253. The cubic root of 28130721 is about 304.1307183971.

The spelling of 28130721 in words is "twenty-eight million, one hundred thirty thousand, seven hundred twenty-one".