661555566 has 96 divisors (see below), whose sum is σ = 1800288000. Its totient is φ = 179054064.

The previous prime is 661555513. The next prime is 661555571. The reversal of 661555566 is 665555166.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 43695 + ... + 56853.

It is an arithmetic number, because the mean of its divisors is an integer number (18753000).

Almost surely, 2^661555566 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661555566, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (900144000).

661555566 is an abundant number, since it is smaller than the sum of its proper divisors (1138732434).

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

661555566 is a wasteful number, since it uses less digits than its factorization.

661555566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13203 (or 13190 counting only the distinct ones).

The product of its digits is 810000, while the sum is 45.

The square root of 661555566 is about 25720.7225015162. The cubic root of 661555566 is about 871.3422562516.

The spelling of 661555566 in words is "six hundred sixty-one million, five hundred fifty-five thousand, five hundred sixty-six".