661666565550 has 96 divisors (see below), whose sum is σ = 1689291637344. Its totient is φ = 171267264000.

The previous prime is 661666565477. The next prime is 661666565557. The reversal of 661666565550 is 55565666166.

661666565550 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661666565557) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 2194960 + ... + 2478140.

It is an arithmetic number, because the mean of its divisors is an integer number (17596787889).

Almost surely, 2^661666565550 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661666565550, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (844645818672).

661666565550 is an abundant number, since it is smaller than the sum of its proper divisors (1027625071794).

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

661666565550 is a wasteful number, since it uses less digits than its factorization.

661666565550 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 283654 (or 283649 counting only the distinct ones).

The product of its (nonzero) digits is 29160000, while the sum is 57.

The spelling of 661666565550 in words is "six hundred sixty-one billion, six hundred sixty-six million, five hundred sixty-five thousand, five hundred fifty".