661566065665 has 4 divisors (see below), whose sum is σ = 793879278804. Its totient is φ = 529252852528.

The previous prime is 661566065653. The next prime is 661566065683. The reversal of 661566065665 is 566560665166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 566560665166 = 2 ⋅283280332583.

It can be written as a sum of positive squares in 2 ways, for example, as 506311941136 + 155254124529 = 711556^2 + 394023^2 .

It is a cyclic number.

It is not a de Polignac number, because 661566065665 - 2¹⁷ = 661565934593 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66156606562 + ... + 66156606571.

It is an arithmetic number, because the mean of its divisors is an integer number (198469819701).

Almost surely, 2^661566065665 is an apocalyptic number.

It is an amenable number.

661566065665 is a deficient number, since it is larger than the sum of its proper divisors (132313213139).

661566065665 is a wasteful number, since it uses less digits than its factorization.

661566065665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132313213138.

The product of its (nonzero) digits is 34992000, while the sum is 58.

The spelling of 661566065665 in words is "six hundred sixty-one billion, five hundred sixty-six million, sixty-five thousand, six hundred sixty-five".