21641543549 has 2 divisors, whose sum is σ = 21641543550. Its totient is φ = 21641543548.

The previous prime is 21641543537. The next prime is 21641543551. The reversal of 21641543549 is 94534514612.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21562866649 + 78676900 = 146843^2 + 8870^2 .

It is a cyclic number.

It is not a de Polignac number, because 21641543549 - 2²⁴ = 21624766333 is a prime.

Together with 21641543551, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21641543849) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10820771774 + 10820771775.

It is an arithmetic number, because the mean of its divisors is an integer number (10820771775).

Almost surely, 2^21641543549 is an apocalyptic number.

It is an amenable number.

21641543549 is a deficient number, since it is larger than the sum of its proper divisors (1).

21641543549 is an equidigital number, since it uses as much as digits as its factorization.

21641543549 is an evil number, because the sum of its binary digits is even.

The product of its digits is 518400, while the sum is 44.

The spelling of 21641543549 in words is "twenty-one billion, six hundred forty-one million, five hundred forty-three thousand, five hundred forty-nine".