21663205051021 has 2 divisors, whose sum is σ = 21663205051022. Its totient is φ = 21663205051020.

The previous prime is 21663205050997. The next prime is 21663205051031. The reversal of 21663205051021 is 12015050236612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19838882095396 + 1824322955625 = 4454086^2 + 1350675^2 .

It is a cyclic number.

It is not a de Polignac number, because 21663205051021 - 2¹⁵ = 21663205018253 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21663205051031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10831602525510 + 10831602525511.

It is an arithmetic number, because the mean of its divisors is an integer number (10831602525511).

Almost surely, 2^{21663205051021} is an apocalyptic number.

It is an amenable number.

21663205051021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21663205051021 is an equidigital number, since it uses as much as digits as its factorization.

21663205051021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 21600, while the sum is 34.

Adding to 21663205051021 its reverse (12015050236612), we get a palindrome (33678255287633).

The spelling of 21663205051021 in words is "twenty-one trillion, six hundred sixty-three billion, two hundred five million, fifty-one thousand, twenty-one".