28721138 has 8 divisors (see below), whose sum is σ = 43500288. Its totient is φ = 14221044.

The previous prime is 28721137. The next prime is 28721171. The reversal of 28721138 is 83112782.

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

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (28721131) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 69506 + ... + 69917.

It is an arithmetic number, because the mean of its divisors is an integer number (5437536).

Almost surely, 2^28721138 is an apocalyptic number.

28721138 is a deficient number, since it is larger than the sum of its proper divisors (14779150).

28721138 is a wasteful number, since it uses less digits than its factorization.

28721138 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 139528.

The product of its digits is 5376, while the sum is 32.

The square root of 28721138 is about 5359.2105761950. The cubic root of 28721138 is about 306.2437362040.

It can be divided in two parts, 287 and 21138, that multiplied together give a palindrome (6066606).

The spelling of 28721138 in words is "twenty-eight million, seven hundred twenty-one thousand, one hundred thirty-eight".