28319981 has 2 divisors, whose sum is σ = 28319982. Its totient is φ = 28319980.

The previous prime is 28319959. The next prime is 28320001. The reversal of 28319981 is 18991382.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 28249225 + 70756 = 5315^2 + 266^2 .

It is a cyclic number.

It is not a de Polignac number, because 28319981 - 2²² = 24125677 is a prime.

It is a super-2 number, since 2×28319981² = 1604042647680722, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (28319281) 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, 14159990 + 14159991.

It is an arithmetic number, because the mean of its divisors is an integer number (14159991).

Almost surely, 2^28319981 is an apocalyptic number.

It is an amenable number.

28319981 is a deficient number, since it is larger than the sum of its proper divisors (1).

28319981 is an equidigital number, since it uses as much as digits as its factorization.

28319981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 31104, while the sum is 41.

The square root of 28319981 is about 5321.6520931004. The cubic root of 28319981 is about 304.8112457474.

The spelling of 28319981 in words is "twenty-eight million, three hundred nineteen thousand, nine hundred eighty-one".