66561899816566 has 16 divisors (see below), whose sum is σ = 124479397059840. Its totient is φ = 25933207720680.

The previous prime is 66561899816563. The next prime is 66561899816593.

66561899816566 is nontrivially palindromic in base 10.

It is a self number, because there is not a number n which added to its sum of digits gives 66561899816566.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66561899816563) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 216110064186 + ... + 216110064493.

It is an arithmetic number, because the mean of its divisors is an integer number (7779962316240).

Almost surely, 2^{66561899816566} is an apocalyptic number.

66561899816566 is a deficient number, since it is larger than the sum of its proper divisors (57917497243274).

66561899816566 is a wasteful number, since it uses less digits than its factorization.

66561899816566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 432220128699.

The product of its digits is 6046617600, while the sum is 82.

The spelling of 66561899816566 in words is "sixty-six trillion, five hundred sixty-one billion, eight hundred ninety-nine million, eight hundred sixteen thousand, five hundred sixty-six".