21173158787321 has 4 divisors (see below), whose sum is σ = 21173169550500. Its totient is φ = 21173148024144.

The previous prime is 21173158787317. The next prime is 21173158787353. The reversal of 21173158787321 is 12378785137112.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 1581027097321 + 19592131690000 = 1257389^2 + 4426300^2 .

It is a cyclic number.

It is not a de Polignac number, because 21173158787321 - 2² = 21173158787317 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21173158787021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1495346 + ... + 6677003.

It is an arithmetic number, because the mean of its divisors is an integer number (5293292387625).

Almost surely, 2^{21173158787321} is an apocalyptic number.

It is an amenable number.

21173158787321 is a deficient number, since it is larger than the sum of its proper divisors (10763179).

21173158787321 is an equidigital number, since it uses as much as digits as its factorization.

21173158787321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10763178.

The product of its digits is 3951360, while the sum is 56.

The spelling of 21173158787321 in words is "twenty-one trillion, one hundred seventy-three billion, one hundred fifty-eight million, seven hundred eighty-seven thousand, three hundred twenty-one".