28647721 has 2 divisors, whose sum is σ = 28647722. Its totient is φ = 28647720.

The previous prime is 28647709. The next prime is 28647727. The reversal of 28647721 is 12774682.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19713600 + 8934121 = 4440^2 + 2989^2 .

It is a cyclic number.

It is not a de Polignac number, because 28647721 - 2⁹ = 28647209 is a prime.

It is not a weakly prime, because it can be changed into another prime (28647727) 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, 14323860 + 14323861.

It is an arithmetic number, because the mean of its divisors is an integer number (14323861).

Almost surely, 2^28647721 is an apocalyptic number.

It is an amenable number.

28647721 is a deficient number, since it is larger than the sum of its proper divisors (1).

28647721 is an equidigital number, since it uses as much as digits as its factorization.

28647721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 37632, while the sum is 37.

The square root of 28647721 is about 5352.3565837862. The cubic root of 28647721 is about 305.9825733736.

It can be divided in two parts, 2864 and 7721, that added together give a triangular number (10585 = T₁₄₅).

The spelling of 28647721 in words is "twenty-eight million, six hundred forty-seven thousand, seven hundred twenty-one".