28209821 has 2 divisors, whose sum is σ = 28209822. Its totient is φ = 28209820.

The previous prime is 28209803. The next prime is 28209827. The reversal of 28209821 is 12890282.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 27772900 + 436921 = 5270^2 + 661^2 .

It is a cyclic number.

It is not a de Polignac number, because 28209821 - 2¹⁴ = 28193437 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (28209827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14104910 + 14104911.

It is an arithmetic number, because the mean of its divisors is an integer number (14104911).

Almost surely, 2^28209821 is an apocalyptic number.

It is an amenable number.

28209821 is a deficient number, since it is larger than the sum of its proper divisors (1).

28209821 is an equidigital number, since it uses as much as digits as its factorization.

28209821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4608, while the sum is 32.

The square root of 28209821 is about 5311.2918390915. The cubic root of 28209821 is about 304.4155105622.

The spelling of 28209821 in words is "twenty-eight million, two hundred nine thousand, eight hundred twenty-one".