21666532549 has 2 divisors, whose sum is σ = 21666532550. Its totient is φ = 21666532548.

The previous prime is 21666532429. The next prime is 21666532567. The reversal of 21666532549 is 94523566612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20351019649 + 1315512900 = 142657^2 + 36270^2 .

It is a cyclic number.

It is not a de Polignac number, because 21666532549 - 2⁹ = 21666532037 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21666532579) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10833266274 + 10833266275.

It is an arithmetic number, because the mean of its divisors is an integer number (10833266275).

Almost surely, 2^21666532549 is an apocalyptic number.

It is an amenable number.

21666532549 is a deficient number, since it is larger than the sum of its proper divisors (1).

21666532549 is an equidigital number, since it uses as much as digits as its factorization.

21666532549 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2332800, while the sum is 49.

The spelling of 21666532549 in words is "twenty-one billion, six hundred sixty-six million, five hundred thirty-two thousand, five hundred forty-nine".