21661042665005 has 4 divisors (see below), whose sum is σ = 25993251198012. Its totient is φ = 17328834132000.

The previous prime is 21661042664929. The next prime is 21661042665007. The reversal of 21661042665005 is 50056624016612.

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 16092830258569 + 5568212406436 = 4011587^2 + 2359706^2 .

It is not a de Polignac number, because 21661042665005 - 2⁴² = 17262996153901 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661042665007) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2166104266496 + ... + 2166104266505.

It is an arithmetic number, because the mean of its divisors is an integer number (6498312799503).

Almost surely, 2^{21661042665005} is an apocalyptic number.

It is an amenable number.

21661042665005 is a deficient number, since it is larger than the sum of its proper divisors (4332208533007).

21661042665005 is an equidigital number, since it uses as much as digits as its factorization.

21661042665005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4332208533006.

The product of its (nonzero) digits is 518400, while the sum is 44.

The spelling of 21661042665005 in words is "twenty-one trillion, six hundred sixty-one billion, forty-two million, six hundred sixty-five thousand, five".