21566943659 has 2 divisors, whose sum is σ = 21566943660. Its totient is φ = 21566943658.

The previous prime is 21566943613. The next prime is 21566943679. The reversal of 21566943659 is 95634966512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21566943659 - 2²⁰ = 21565895083 is a prime.

It is not a weakly prime, because it can be changed into another prime (21566943679) 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, 10783471829 + 10783471830.

It is an arithmetic number, because the mean of its divisors is an integer number (10783471830).

Almost surely, 2^21566943659 is an apocalyptic number.

21566943659 is a deficient number, since it is larger than the sum of its proper divisors (1).

21566943659 is an equidigital number, since it uses as much as digits as its factorization.

21566943659 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10497600, while the sum is 56.

The spelling of 21566943659 in words is "twenty-one billion, five hundred sixty-six million, nine hundred forty-three thousand, six hundred fifty-nine".