661818308718661 has 2 divisors, whose sum is σ = 661818308718662. Its totient is φ = 661818308718660.

The previous prime is 661818308718659. The next prime is 661818308718673. The reversal of 661818308718661 is 166817803818166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 336686021188036 + 325132287530625 = 18349006^2 + 18031425^2 .

It is a cyclic number.

It is not a de Polignac number, because 661818308718661 - 2¹ = 661818308718659 is a prime.

Together with 661818308718659, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661818308715661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330909154359330 + 330909154359331.

It is an arithmetic number, because the mean of its divisors is an integer number (330909154359331).

Almost surely, 2^{661818308718661} is an apocalyptic number.

It is an amenable number.

661818308718661 is a deficient number, since it is larger than the sum of its proper divisors (1).

661818308718661 is an equidigital number, since it uses as much as digits as its factorization.

661818308718661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 111476736, while the sum is 70.

The spelling of 661818308718661 in words is "six hundred sixty-one trillion, eight hundred eighteen billion, three hundred eight million, seven hundred eighteen thousand, six hundred sixty-one".