20671165661 has 4 divisors (see below), whose sum is σ = 21229845852. Its totient is φ = 20112485472.

The previous prime is 20671165639. The next prime is 20671165681. The reversal of 20671165661 is 16656117602.

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 7630896025 + 13040269636 = 87355^2 + 114194^2 .

It is a cyclic number.

It is not a de Polignac number, because 20671165661 - 2²² = 20666971357 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20671165631) 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 3 ways as a sum of consecutive naturals, for example, 279340040 + ... + 279340113.

It is an arithmetic number, because the mean of its divisors is an integer number (5307461463).

Almost surely, 2^20671165661 is an apocalyptic number.

It is an amenable number.

20671165661 is a deficient number, since it is larger than the sum of its proper divisors (558680191).

20671165661 is an equidigital number, since it uses as much as digits as its factorization.

20671165661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 558680190.

The product of its (nonzero) digits is 90720, while the sum is 41.

The spelling of 20671165661 in words is "twenty billion, six hundred seventy-one million, one hundred sixty-five thousand, six hundred sixty-one".