28138681 has 4 divisors (see below), whose sum is σ = 28155172. Its totient is φ = 28122192.

The previous prime is 28138679. The next prime is 28138687. The reversal of 28138681 is 18683182.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11451456 + 16687225 = 3384^2 + 4085^2 .

It is a cyclic number.

It is not a de Polignac number, because 28138681 - 2¹ = 28138679 is a prime.

It is a super-2 number, since 2×28138681² = 1583570736839522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 28138681.

It is not an unprimeable number, because it can be changed into a prime (28138687) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5346 + ... + 9211.

It is an arithmetic number, because the mean of its divisors is an integer number (7038793).

Almost surely, 2^28138681 is an apocalyptic number.

It is an amenable number.

28138681 is a deficient number, since it is larger than the sum of its proper divisors (16491).

28138681 is a wasteful number, since it uses less digits than its factorization.

28138681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16490.

The product of its digits is 18432, while the sum is 37.

The square root of 28138681 is about 5304.5905591290. The cubic root of 28138681 is about 304.1594017739.

The spelling of 28138681 in words is "twenty-eight million, one hundred thirty-eight thousand, six hundred eighty-one".