28680721 has 2 divisors, whose sum is σ = 28680722. Its totient is φ = 28680720.

The previous prime is 28680697. The next prime is 28680749. The reversal of 28680721 is 12708682.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16000000 + 12680721 = 4000^2 + 3561^2 .

It is a cyclic number.

It is not a de Polignac number, because 28680721 - 2⁷ = 28680593 is a prime.

It is a super-3 number, since 3×28680721³ (a number of 23 digits) contains 333 as substring.

It is not a weakly prime, because it can be changed into another prime (28680761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14340360 + 14340361.

It is an arithmetic number, because the mean of its divisors is an integer number (14340361).

Almost surely, 2^28680721 is an apocalyptic number.

It is an amenable number.

28680721 is a deficient number, since it is larger than the sum of its proper divisors (1).

28680721 is an equidigital number, since it uses as much as digits as its factorization.

28680721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10752, while the sum is 34.

The square root of 28680721 is about 5355.4384507713. The cubic root of 28680721 is about 306.1000178554.

The spelling of 28680721 in words is "twenty-eight million, six hundred eighty thousand, seven hundred twenty-one".