21555322121 has 4 divisors (see below), whose sum is σ = 21635453700. Its totient is φ = 21475190544.

The previous prime is 21555322097. The next prime is 21555322127. The reversal of 21555322121 is 12122355512.

It is a happy number.

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 2587146496 + 18968175625 = 50864^2 + 137725^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21555322121 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21555322127) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40065386 + ... + 40065923.

It is an arithmetic number, because the mean of its divisors is an integer number (5408863425).

Almost surely, 2^21555322121 is an apocalyptic number.

It is an amenable number.

21555322121 is a deficient number, since it is larger than the sum of its proper divisors (80131579).

21555322121 is an equidigital number, since it uses as much as digits as its factorization.

21555322121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80131578.

The product of its digits is 6000, while the sum is 29.

Adding to 21555322121 its reverse (12122355512), we get a palindrome (33677677633).

The spelling of 21555322121 in words is "twenty-one billion, five hundred fifty-five million, three hundred twenty-two thousand, one hundred twenty-one".