21660506566571 has 2 divisors, whose sum is σ = 21660506566572. Its totient is φ = 21660506566570.

The previous prime is 21660506566553. The next prime is 21660506566597. The reversal of 21660506566571 is 17566560506612.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21660506566571 - 2¹⁰ = 21660506565547 is a prime.

It is not a weakly prime, because it can be changed into another prime (21660506566271) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830253283285 + 10830253283286.

It is an arithmetic number, because the mean of its divisors is an integer number (10830253283286).

Almost surely, 2^{21660506566571} is an apocalyptic number.

21660506566571 is a deficient number, since it is larger than the sum of its proper divisors (1).

21660506566571 is an equidigital number, since it uses as much as digits as its factorization.

21660506566571 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 13608000, while the sum is 56.

The spelling of 21660506566571 in words is "twenty-one trillion, six hundred sixty billion, five hundred six million, five hundred sixty-six thousand, five hundred seventy-one".