21563231634521 has 2 divisors, whose sum is σ = 21563231634522. Its totient is φ = 21563231634520.

The previous prime is 21563231634443. The next prime is 21563231634523. The reversal of 21563231634521 is 12543613236512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19835087395600 + 1728144238921 = 4453660^2 + 1314589^2 .

It is a cyclic number.

It is not a de Polignac number, because 21563231634521 - 2¹⁰ = 21563231633497 is a prime.

Together with 21563231634523, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21563231634523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10781615817260 + 10781615817261.

It is an arithmetic number, because the mean of its divisors is an integer number (10781615817261).

Almost surely, 2^{21563231634521} is an apocalyptic number.

It is an amenable number.

21563231634521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21563231634521 is an equidigital number, since it uses as much as digits as its factorization.

21563231634521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 777600, while the sum is 44.

The spelling of 21563231634521 in words is "twenty-one trillion, five hundred sixty-three billion, two hundred thirty-one million, six hundred thirty-four thousand, five hundred twenty-one".