28131665 has 4 divisors (see below), whose sum is σ = 33758004. Its totient is φ = 22505328.

The previous prime is 28131661. The next prime is 28131671. The reversal of 28131665 is 56613182.

It is a happy number.

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 6713281 + 21418384 = 2591^2 + 4628^2 .

It is a cyclic number.

It is not a de Polignac number, because 28131665 - 2² = 28131661 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28131661) 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 in 3 ways as a sum of consecutive naturals, for example, 2813162 + ... + 2813171.

It is an arithmetic number, because the mean of its divisors is an integer number (8439501).

Almost surely, 2^28131665 is an apocalyptic number.

It is an amenable number.

28131665 is a deficient number, since it is larger than the sum of its proper divisors (5626339).

28131665 is an equidigital number, since it uses as much as digits as its factorization.

28131665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5626338.

The product of its digits is 8640, while the sum is 32.

The square root of 28131665 is about 5303.9292039016. The cubic root of 28131665 is about 304.1341203265.

The spelling of 28131665 in words is "twenty-eight million, one hundred thirty-one thousand, six hundred sixty-five".