28778217721 has 24 divisors (see below), whose sum is σ = 32004180000. Its totient is φ = 25663334400.

The previous prime is 28778217707. The next prime is 28778217733. The reversal of 28778217721 is 12771287782.

It is a happy number.

It is not a de Polignac number, because 28778217721 - 2¹¹ = 28778215673 is a prime.

It is a Smith number, since the sum of its digits (52) coincides with the sum of the digits of its prime factors.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28778217751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 20423865 + ... + 20425273.

It is an arithmetic number, because the mean of its divisors is an integer number (1333507500).

Almost surely, 2^28778217721 is an apocalyptic number.

It is an amenable number.

28778217721 is a deficient number, since it is larger than the sum of its proper divisors (3225962279).

28778217721 is a wasteful number, since it uses less digits than its factorization.

28778217721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2041 (or 1980 counting only the distinct ones).

The product of its digits is 1229312, while the sum is 52.

It can be divided in two parts, 287782 and 17721, that added together give a palindrome (305503).

The spelling of 28778217721 in words is "twenty-eight billion, seven hundred seventy-eight million, two hundred seventeen thousand, seven hundred twenty-one".