21143656321 has 4 divisors (see below), whose sum is σ = 21154710852. Its totient is φ = 21132601792.

The previous prime is 21143656297. The next prime is 21143656343. The reversal of 21143656321 is 12365634112.

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 14625516096 + 6518140225 = 120936^2 + 80735^2 .

It is a cyclic number.

It is not a de Polignac number, because 21143656321 - 2³³ = 12553721729 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21143656621) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5524396 + ... + 5528221.

It is an arithmetic number, because the mean of its divisors is an integer number (5288677713).

Almost surely, 2^21143656321 is an apocalyptic number.

It is an amenable number.

21143656321 is a deficient number, since it is larger than the sum of its proper divisors (11054531).

21143656321 is a wasteful number, since it uses less digits than its factorization.

21143656321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11054530.

The product of its digits is 25920, while the sum is 34.

The spelling of 21143656321 in words is "twenty-one billion, one hundred forty-three million, six hundred fifty-six thousand, three hundred twenty-one".