66561319917 has 8 divisors (see below), whose sum is σ = 98609362880. Its totient is φ = 44374213260.

The previous prime is 66561319873. The next prime is 66561319997. The reversal of 66561319917 is 71991316566.

It is a happy number.

66561319917 is a `hidden beast` number, since 6 + 6 + 5 + 613 + 1 + 9 + 9 + 17 = 666.

It is not a de Polignac number, because 66561319917 - 2¹⁰ = 66561318893 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66561319997) 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, 1232617009 + ... + 1232617062.

It is an arithmetic number, because the mean of its divisors is an integer number (12326170360).

Almost surely, 2^66561319917 is an apocalyptic number.

It is an amenable number.

66561319917 is a deficient number, since it is larger than the sum of its proper divisors (32048042963).

66561319917 is a wasteful number, since it uses less digits than its factorization.

66561319917 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2465234080 (or 2465234074 counting only the distinct ones).

The product of its digits is 1837080, while the sum is 54.

The spelling of 66561319917 in words is "sixty-six billion, five hundred sixty-one million, three hundred nineteen thousand, nine hundred seventeen".