28780921 has 8 divisors (see below), whose sum is σ = 31076360. Its totient is φ = 26497152.

The previous prime is 28780919. The next prime is 28780933. The reversal of 28780921 is 12908782.

It can be written as a sum of positive squares in 4 ways, for example, as 2371600 + 26409321 = 1540^2 + 5139^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 28780921 - 2¹ = 28780919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28780901) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2611 + ... + 8023.

It is an arithmetic number, because the mean of its divisors is an integer number (3884545).

Almost surely, 2^28780921 is an apocalyptic number.

It is an amenable number.

28780921 is a deficient number, since it is larger than the sum of its proper divisors (2295439).

28780921 is a wasteful number, since it uses less digits than its factorization.

28780921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5835.

The product of its (nonzero) digits is 16128, while the sum is 37.

The square root of 28780921 is about 5364.7852706329. The cubic root of 28780921 is about 306.4560708863.

The spelling of 28780921 in words is "twenty-eight million, seven hundred eighty thousand, nine hundred twenty-one".