661555506665 has 16 divisors (see below), whose sum is σ = 819501090816. Its totient is φ = 512155828800.

The previous prime is 661555506643. The next prime is 661555506779. The reversal of 661555506665 is 566605555166.

It is not a de Polignac number, because 661555506665 - 2¹⁰ = 661555505641 is a prime.

It is a Smith number, since the sum of its digits (56) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661555506665.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7835264 + ... + 7919246.

It is an arithmetic number, because the mean of its divisors is an integer number (51218818176).

Almost surely, 2^661555506665 is an apocalyptic number.

It is an amenable number.

661555506665 is a deficient number, since it is larger than the sum of its proper divisors (157945584151).

661555506665 is a wasteful number, since it uses less digits than its factorization.

661555506665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 134840.

The product of its (nonzero) digits is 24300000, while the sum is 56.

The spelling of 661555506665 in words is "six hundred sixty-one billion, five hundred fifty-five million, five hundred six thousand, six hundred sixty-five".