21621343565165 has 4 divisors (see below), whose sum is σ = 25945612278204. Its totient is φ = 17297074852128.

The previous prime is 21621343565147. The next prime is 21621343565167. The reversal of 21621343565165 is 56156534312612.

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

It can be written as a sum of positive squares in 2 ways, for example, as 7574461726276 + 14046881838889 = 2752174^2 + 3747917^2 .

It is a cyclic number.

It is not a de Polignac number, because 21621343565165 - 2³² = 21617048597869 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621343565167) 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, 2162134356512 + ... + 2162134356521.

It is an arithmetic number, because the mean of its divisors is an integer number (6486403069551).

Almost surely, 2^{21621343565165} is an apocalyptic number.

It is an amenable number.

21621343565165 is a deficient number, since it is larger than the sum of its proper divisors (4324268713039).

21621343565165 is an equidigital number, since it uses as much as digits as its factorization.

21621343565165 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4324268713038.

The product of its digits is 3888000, while the sum is 50.

Adding to 21621343565165 its reverse (56156534312612), we get a palindrome (77777877877777).

The spelling of 21621343565165 in words is "twenty-one trillion, six hundred twenty-one billion, three hundred forty-three million, five hundred sixty-five thousand, one hundred sixty-five".