1661065561805 has 8 divisors (see below), whose sum is σ = 2146607803032. Its totient is φ = 1226633030208.

The previous prime is 1661065561739. The next prime is 1661065561843. The reversal of 1661065561805 is 5081655601661.

It can be written as a sum of positive squares in 4 ways, for example, as 16018192969 + 1645047368836 = 126563^2 + 1282594^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1661065561805 - 2¹² = 1661065557709 is a prime.

It is a super-2 number, since 2×1661065561805² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12777427334 + ... + 12777427463.

It is an arithmetic number, because the mean of its divisors is an integer number (268325975379).

Almost surely, 2^{1661065561805} is an apocalyptic number.

It is an amenable number.

1661065561805 is a deficient number, since it is larger than the sum of its proper divisors (485542241227).

1661065561805 is a wasteful number, since it uses less digits than its factorization.

1661065561805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25554854815.

The product of its (nonzero) digits is 1296000, while the sum is 50.

The spelling of 1661065561805 in words is "one trillion, six hundred sixty-one billion, sixty-five million, five hundred sixty-one thousand, eight hundred five".