28212721 has 2 divisors, whose sum is σ = 28212722. Its totient is φ = 28212720.

The previous prime is 28212719. The next prime is 28212731. The reversal of 28212721 is 12721282.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 28143025 + 69696 = 5305^2 + 264^2 .

It is a cyclic number.

It is not a de Polignac number, because 28212721 - 2¹ = 28212719 is a prime.

Together with 28212719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (28212731) 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 as a sum of consecutive naturals, namely, 14106360 + 14106361.

It is an arithmetic number, because the mean of its divisors is an integer number (14106361).

Almost surely, 2^28212721 is an apocalyptic number.

It is an amenable number.

28212721 is a deficient number, since it is larger than the sum of its proper divisors (1).

28212721 is an equidigital number, since it uses as much as digits as its factorization.

28212721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 896, while the sum is 25.

The square root of 28212721 is about 5311.5648353381. The cubic root of 28212721 is about 304.4259416190.

The spelling of 28212721 in words is "twenty-eight million, two hundred twelve thousand, seven hundred twenty-one".