28721811 has 4 divisors (see below), whose sum is σ = 38295752. Its totient is φ = 19147872.

The previous prime is 28721809. The next prime is 28721831. The reversal of 28721811 is 11812782.

It is a happy number.

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

It is not a de Polignac number, because 28721811 - 2¹ = 28721809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28721831) 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, 4786966 + ... + 4786971.

It is an arithmetic number, because the mean of its divisors is an integer number (9573938).

Almost surely, 2^28721811 is an apocalyptic number.

28721811 is a deficient number, since it is larger than the sum of its proper divisors (9573941).

28721811 is an equidigital number, since it uses as much as digits as its factorization.

28721811 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9573940.

The product of its digits is 1792, while the sum is 30.

The square root of 28721811 is about 5359.2733649255. The cubic root of 28721811 is about 306.2461281754.

The spelling of 28721811 in words is "twenty-eight million, seven hundred twenty-one thousand, eight hundred eleven".