28189981 has 2 divisors, whose sum is σ = 28189982. Its totient is φ = 28189980.

The previous prime is 28189979. The next prime is 28190017. The reversal of 28189981 is 18998182.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 27657081 + 532900 = 5259^2 + 730^2 .

It is a cyclic number.

It is not a de Polignac number, because 28189981 - 2¹ = 28189979 is a prime.

It is a super-2 number, since 2×28189981² = 1589350057560722, which contains 22 as substring.

Together with 28189979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (28189921) 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 as a sum of consecutive naturals, namely, 14094990 + 14094991.

It is an arithmetic number, because the mean of its divisors is an integer number (14094991).

Almost surely, 2^28189981 is an apocalyptic number.

It is an amenable number.

28189981 is a deficient number, since it is larger than the sum of its proper divisors (1).

28189981 is an equidigital number, since it uses as much as digits as its factorization.

28189981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 82944, while the sum is 46.

The square root of 28189981 is about 5309.4237917122. The cubic root of 28189981 is about 304.3441285641.

The spelling of 28189981 in words is "twenty-eight million, one hundred eighty-nine thousand, nine hundred eighty-one".