28981317721 has 2 divisors, whose sum is σ = 28981317722. Its totient is φ = 28981317720.

The previous prime is 28981317713. The next prime is 28981317733. The reversal of 28981317721 is 12771318982.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 28019077321 + 962240400 = 167389^2 + 31020^2 .

It is a cyclic number.

It is not a de Polignac number, because 28981317721 - 2³ = 28981317713 is a prime.

It is not a weakly prime, because it can be changed into another prime (28981314721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14490658860 + 14490658861.

It is an arithmetic number, because the mean of its divisors is an integer number (14490658861).

Almost surely, 2^28981317721 is an apocalyptic number.

It is an amenable number.

28981317721 is a deficient number, since it is larger than the sum of its proper divisors (1).

28981317721 is an equidigital number, since it uses as much as digits as its factorization.

28981317721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 338688, while the sum is 49.

The spelling of 28981317721 in words is "twenty-eight billion, nine hundred eighty-one million, three hundred seventeen thousand, seven hundred twenty-one".