28723921 has 4 divisors (see below), whose sum is σ = 28790692. Its totient is φ = 28657152.

The previous prime is 28723913. The next prime is 28723943. The reversal of 28723921 is 12932782.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8473921 + 20250000 = 2911^2 + 4500^2 .

It is a cyclic number.

It is not a de Polignac number, because 28723921 - 2³ = 28723913 is a prime.

It is a super-2 number, since 2×28723921² = 1650127275228482, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28720921) 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 3 ways as a sum of consecutive naturals, for example, 32736 + ... + 33601.

It is an arithmetic number, because the mean of its divisors is an integer number (7197673).

Almost surely, 2^28723921 is an apocalyptic number.

It is an amenable number.

28723921 is a deficient number, since it is larger than the sum of its proper divisors (66771).

28723921 is an equidigital number, since it uses as much as digits as its factorization.

28723921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 66770.

The product of its digits is 12096, while the sum is 34.

The square root of 28723921 is about 5359.4702163553. The cubic root of 28723921 is about 306.2536272790.

The spelling of 28723921 in words is "twenty-eight million, seven hundred twenty-three thousand, nine hundred twenty-one".