28721815 has 8 divisors (see below), whose sum is σ = 34557120. Its totient is φ = 22916832.

The previous prime is 28721809. The next prime is 28721831. The reversal of 28721815 is 51812782.

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-28721815 is a prime.

It is a congruent number.

It is an unprimeable number.

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, 5439 + ... + 9328.

It is an arithmetic number, because the mean of its divisors is an integer number (4319640).

Almost surely, 2^28721815 is an apocalyptic number.

28721815 is a deficient number, since it is larger than the sum of its proper divisors (5835305).

28721815 is a wasteful number, since it uses less digits than its factorization.

28721815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15161.

The product of its digits is 8960, while the sum is 34.

The square root of 28721815 is about 5359.2737381104. The cubic root of 28721815 is about 306.2461423921.

The spelling of 28721815 in words is "twenty-eight million, seven hundred twenty-one thousand, eight hundred fifteen".