1665265561 has 8 divisors (see below), whose sum is σ = 1707051240. Its totient is φ = 1623992832.

The previous prime is 1665265543. The next prime is 1665265577. The reversal of 1665265561 is 1655625661.

1665265561 = T₆₇₁₈ + T₆₇₁₉ + ... + T₆₇₉₀.

It can be written as a sum of positive squares in 4 ways, for example, as 12355225 + 1652910336 = 3515^2 + 40656^2 .

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 1665265561 - 2¹¹ = 1665263513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1665265531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 121660 + ... + 134653.

It is an arithmetic number, because the mean of its divisors is an integer number (213381405).

Almost surely, 2^1665265561 is an apocalyptic number.

It is an amenable number.

1665265561 is a deficient number, since it is larger than the sum of its proper divisors (41785679).

1665265561 is an equidigital number, since it uses as much as digits as its factorization.

1665265561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 256475.

The product of its digits is 324000, while the sum is 43.

The square root of 1665265561 is about 40807.6654686347. The cubic root of 1665265561 is about 1185.2987694618.

The spelling of 1665265561 in words is "one billion, six hundred sixty-five million, two hundred sixty-five thousand, five hundred sixty-one".