21668663657653 has 2 divisors, whose sum is σ = 21668663657654. Its totient is φ = 21668663657652.

The previous prime is 21668663657647. The next prime is 21668663657699. The reversal of 21668663657653 is 35675636686612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19227891741444 + 2440771916209 = 4384962^2 + 1562297^2 .

It is a cyclic number.

It is not a de Polignac number, because 21668663657653 - 2⁵ = 21668663657621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21668663657353) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10834331828826 + 10834331828827.

It is an arithmetic number, because the mean of its divisors is an integer number (10834331828827).

Almost surely, 2^{21668663657653} is an apocalyptic number.

It is an amenable number.

21668663657653 is a deficient number, since it is larger than the sum of its proper divisors (1).

21668663657653 is an equidigital number, since it uses as much as digits as its factorization.

21668663657653 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1175731200, while the sum is 70.

The spelling of 21668663657653 in words is "twenty-one trillion, six hundred sixty-eight billion, six hundred sixty-three million, six hundred fifty-seven thousand, six hundred fifty-three".