21605311361 has 2 divisors, whose sum is σ = 21605311362. Its totient is φ = 21605311360.

The previous prime is 21605311327. The next prime is 21605311363. The reversal of 21605311361 is 16311350612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14515671361 + 7089640000 = 120481^2 + 84200^2 .

It is a cyclic number.

It is not a de Polignac number, because 21605311361 - 2⁶ = 21605311297 is a prime.

It is a Sophie Germain prime.

Together with 21605311363, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21605311363) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802655680 + 10802655681.

It is an arithmetic number, because the mean of its divisors is an integer number (10802655681).

Almost surely, 2^21605311361 is an apocalyptic number.

It is an amenable number.

21605311361 is a deficient number, since it is larger than the sum of its proper divisors (1).

21605311361 is an equidigital number, since it uses as much as digits as its factorization.

21605311361 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3240, while the sum is 29.

Adding to 21605311361 its reverse (16311350612), we get a palindrome (37916661973).

The spelling of 21605311361 in words is "twenty-one billion, six hundred five million, three hundred eleven thousand, three hundred sixty-one".