20665220161 has 4 divisors (see below), whose sum is σ = 21003994324. Its totient is φ = 20326446000.

The previous prime is 20665220143. The next prime is 20665220183. The reversal of 20665220161 is 16102256602.

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 7015737600 + 13649482561 = 83760^2 + 116831^2 .

It is a cyclic number.

It is not a de Polignac number, because 20665220161 - 2⁵ = 20665220129 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20665220561) by changing a digit.

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, 169386990 + ... + 169387111.

It is an arithmetic number, because the mean of its divisors is an integer number (5250998581).

Almost surely, 2^20665220161 is an apocalyptic number.

It is an amenable number.

20665220161 is a deficient number, since it is larger than the sum of its proper divisors (338774163).

20665220161 is an equidigital number, since it uses as much as digits as its factorization.

20665220161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 338774162.

The product of its (nonzero) digits is 8640, while the sum is 31.

Adding to 20665220161 its reverse (16102256602), we get a palindrome (36767476763).

The spelling of 20665220161 in words is "twenty billion, six hundred sixty-five million, two hundred twenty thousand, one hundred sixty-one".