28718721 has 6 divisors (see below), whose sum is σ = 41482610. Its totient is φ = 19145808.

The previous prime is 28718717. The next prime is 28718731. The reversal of 28718721 is 12781782.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 22667121 + 6051600 = 4761^2 + 2460^2 .

It is not a de Polignac number, because 28718721 - 2² = 28718717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28718731) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1595476 + ... + 1595493.

Almost surely, 2^28718721 is an apocalyptic number.

It is an amenable number.

28718721 is a deficient number, since it is larger than the sum of its proper divisors (12763889).

28718721 is a wasteful number, since it uses less digits than its factorization.

28718721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3190975 (or 3190972 counting only the distinct ones).

The product of its digits is 12544, while the sum is 36.

The square root of 28718721 is about 5358.9850718210. The cubic root of 28718721 is about 306.2351454130.

The spelling of 28718721 in words is "twenty-eight million, seven hundred eighteen thousand, seven hundred twenty-one".