21661447121 has 4 divisors (see below), whose sum is σ = 21786657972. Its totient is φ = 21536236272.

The previous prime is 21661447051. The next prime is 21661447133. The reversal of 21661447121 is 12174416612.

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 17747568400 + 3913878721 = 133220^2 + 62561^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661447121 - 2¹⁰ = 21661446097 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21661440121) 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, 62605166 + ... + 62605511.

It is an arithmetic number, because the mean of its divisors is an integer number (5446664493).

Almost surely, 2^21661447121 is an apocalyptic number.

It is an amenable number.

21661447121 is a deficient number, since it is larger than the sum of its proper divisors (125210851).

21661447121 is a wasteful number, since it uses less digits than its factorization.

21661447121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 125210850.

The product of its digits is 16128, while the sum is 35.

The spelling of 21661447121 in words is "twenty-one billion, six hundred sixty-one million, four hundred forty-seven thousand, one hundred twenty-one".