28991989 has 4 divisors (see below), whose sum is σ = 31222156. Its totient is φ = 26761824.

The previous prime is 28991981. The next prime is 28991993. The reversal of 28991989 is 98919982.

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 11628100 + 17363889 = 3410^2 + 4167^2 .

It is a cyclic number.

It is not a de Polignac number, because 28991989 - 2³ = 28991981 is a prime.

It is a super-2 number, since 2×28991989² = 1681070852352242, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28991981) 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, 1115064 + ... + 1115089.

It is an arithmetic number, because the mean of its divisors is an integer number (7805539).

Almost surely, 2^28991989 is an apocalyptic number.

It is an amenable number.

28991989 is a deficient number, since it is larger than the sum of its proper divisors (2230167).

28991989 is a wasteful number, since it uses less digits than its factorization.

28991989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2230166.

The product of its digits is 839808, while the sum is 55.

The square root of 28991989 is about 5384.4209530831. The cubic root of 28991989 is about 307.2033899286.

The spelling of 28991989 in words is "twenty-eight million, nine hundred ninety-one thousand, nine hundred eighty-nine".