28131881 has 2 divisors, whose sum is σ = 28131882. Its totient is φ = 28131880.

The previous prime is 28131871. The next prime is 28131899. The reversal of 28131881 is 18813182.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17347225 + 10784656 = 4165^2 + 3284^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-28131881 is a prime.

It is a super-2 number, since 2×28131881² = 1582805457196322, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is equal to p_1749119 and since 28131881 and 1749119 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (28131811) 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, 14065940 + 14065941.

It is an arithmetic number, because the mean of its divisors is an integer number (14065941).

Almost surely, 2^28131881 is an apocalyptic number.

It is an amenable number.

28131881 is a deficient number, since it is larger than the sum of its proper divisors (1).

28131881 is an equidigital number, since it uses as much as digits as its factorization.

28131881 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3072, while the sum is 32.

The square root of 28131881 is about 5303.9495661252. The cubic root of 28131881 is about 304.1348987234.

The spelling of 28131881 in words is "twenty-eight million, one hundred thirty-one thousand, eight hundred eighty-one".