28530991 has 4 divisors (see below), whose sum is σ = 28548184. Its totient is φ = 28513800.

The previous prime is 28530979. The next prime is 28531051. The reversal of 28530991 is 19903582.

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

It is a cyclic number.

It is not a de Polignac number, because 28530991 - 2⁹ = 28530479 is a prime.

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 28530991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28530911) 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, 5805 + ... + 9526.

It is an arithmetic number, because the mean of its divisors is an integer number (7137046).

Almost surely, 2^28530991 is an apocalyptic number.

28530991 is a deficient number, since it is larger than the sum of its proper divisors (17193).

28530991 is a wasteful number, since it uses less digits than its factorization.

28530991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17192.

The product of its (nonzero) digits is 19440, while the sum is 37.

The square root of 28530991 is about 5341.4409104660. The cubic root of 28530991 is about 305.5664149872.

The spelling of 28530991 in words is "twenty-eight million, five hundred thirty thousand, nine hundred ninety-one".