66551815566 has 128 divisors (see below), whose sum is σ = 155295360000. Its totient is φ = 21104468352.

The previous prime is 66551815553. The next prime is 66551815571.

It is a happy number.

66551815566 is a `hidden beast` number, since 6 + 6 + 5 + 5 + 1 + 81 + 556 + 6 = 666.

66551815566 is nontrivially palindromic in base 10.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 23457100 + ... + 23459936.

It is an arithmetic number, because the mean of its divisors is an integer number (1213245000).

Almost surely, 2^66551815566 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 66551815566, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (77647680000).

66551815566 is an abundant number, since it is smaller than the sum of its proper divisors (88743544434).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

66551815566 is a wasteful number, since it uses less digits than its factorization.

66551815566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3143 (or 3137 counting only the distinct ones).

The product of its digits is 6480000, while the sum is 54.

The spelling of 66551815566 in words is "sixty-six billion, five hundred fifty-one million, eight hundred fifteen thousand, five hundred sixty-six".