661641564665 has 4 divisors (see below), whose sum is σ = 793969877604. Its totient is φ = 529313251728.

The previous prime is 661641564631. The next prime is 661641564707. The reversal of 661641564665 is 566465146166.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 165590397184 + 496051167481 = 406928^2 + 704309^2 .

It is a cyclic number.

It is not a de Polignac number, because 661641564665 - 2⁶ = 661641564601 is a prime.

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 661641564665.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66164156462 + ... + 66164156471.

It is an arithmetic number, because the mean of its divisors is an integer number (198492469401).

Almost surely, 2^661641564665 is an apocalyptic number.

It is an amenable number.

661641564665 is a deficient number, since it is larger than the sum of its proper divisors (132328312939).

661641564665 is a wasteful number, since it uses less digits than its factorization.

661641564665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 132328312938.

The product of its digits is 18662400, while the sum is 56.

The spelling of 661641564665 in words is "six hundred sixty-one billion, six hundred forty-one million, five hundred sixty-four thousand, six hundred sixty-five".