28719721 has 8 divisors (see below), whose sum is σ = 29640744. Its totient is φ = 27809280.

The previous prime is 28719707. The next prime is 28719731. The reversal of 28719721 is 12791782.

It can be written as a sum of positive squares in 4 ways, for example, as 1010025 + 27709696 = 1005^2 + 5264^2 .

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-28719721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28719701) 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, 3061 + ... + 8173.

It is an arithmetic number, because the mean of its divisors is an integer number (3705093).

Almost surely, 2^28719721 is an apocalyptic number.

It is an amenable number.

28719721 is a deficient number, since it is larger than the sum of its proper divisors (921023).

28719721 is a wasteful number, since it uses less digits than its factorization.

28719721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5291.

The product of its digits is 14112, while the sum is 37.

The square root of 28719721 is about 5359.0783722577. The cubic root of 28719721 is about 306.2386997913.

The spelling of 28719721 in words is "twenty-eight million, seven hundred nineteen thousand, seven hundred twenty-one".