28731721 has 8 divisors (see below), whose sum is σ = 30526920. Its totient is φ = 26990208.

The previous prime is 28731713. The next prime is 28731727. The reversal of 28731721 is 12713782.

It can be written as a sum of positive squares in 4 ways, for example, as 5112121 + 23619600 = 2261^2 + 4860^2 .

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 28731721 - 2³ = 28731713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28731727) 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, 12316 + ... + 14461.

It is an arithmetic number, because the mean of its divisors is an integer number (3815865).

Almost surely, 2^28731721 is an apocalyptic number.

It is an amenable number.

28731721 is a deficient number, since it is larger than the sum of its proper divisors (1795199).

28731721 is a wasteful number, since it uses less digits than its factorization.

28731721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26843.

The product of its digits is 4704, while the sum is 31.

The square root of 28731721 is about 5360.1978508260. The cubic root of 28731721 is about 306.2813458961.

The spelling of 28731721 in words is "twenty-eight million, seven hundred thirty-one thousand, seven hundred twenty-one".