1665661101561 has 12 divisors (see below), whose sum is σ = 2488918887780. Its totient is φ = 1072149674400.

The previous prime is 1665661101557. The next prime is 1665661101563. The reversal of 1665661101561 is 1651011665661.

1665661101561 is a `hidden beast` number, since 1 + 6 + 6 + 566 + 1 + 10 + 15 + 61 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 832712825961 + 832948275600 = 912531^2 + 912660^2 .

It is not a de Polignac number, because 1665661101561 - 2² = 1665661101557 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1665661101563) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3190921390 + ... + 3190921911.

It is an arithmetic number, because the mean of its divisors is an integer number (207409907315).

Almost surely, 2^{1665661101561} is an apocalyptic number.

It is an amenable number.

1665661101561 is a deficient number, since it is larger than the sum of its proper divisors (823257786219).

1665661101561 is a wasteful number, since it uses less digits than its factorization.

1665661101561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6381843336 (or 6381843333 counting only the distinct ones).

The product of its (nonzero) digits is 194400, while the sum is 45.

The spelling of 1665661101561 in words is "one trillion, six hundred sixty-five billion, six hundred sixty-one million, one hundred one thousand, five hundred sixty-one".