21661321161 has 8 divisors (see below), whose sum is σ = 29877684480. Its totient is φ = 13942919312.

The previous prime is 21661321151. The next prime is 21661321163. The reversal of 21661321161 is 16112316612.

It is a happy number.

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 21661321161 - 2¹⁵ = 21661288393 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21661321163) 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, 124490265 + ... + 124490438.

It is an arithmetic number, because the mean of its divisors is an integer number (3734710560).

Almost surely, 2^21661321161 is an apocalyptic number.

It is an amenable number.

21661321161 is a deficient number, since it is larger than the sum of its proper divisors (8216363319).

21661321161 is a wasteful number, since it uses less digits than its factorization.

21661321161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 248980735.

The product of its digits is 2592, while the sum is 30.

Adding to 21661321161 its reverse (16112316612), we get a palindrome (37773637773).

The spelling of 21661321161 in words is "twenty-one billion, six hundred sixty-one million, three hundred twenty-one thousand, one hundred sixty-one".