21688981321 has 4 divisors (see below), whose sum is σ = 24787407232. Its totient is φ = 18590555412.

The previous prime is 21688981283. The next prime is 21688981357. The reversal of 21688981321 is 12318988612.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21688981321 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21688984321) 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, 1549212945 + ... + 1549212958.

It is an arithmetic number, because the mean of its divisors is an integer number (6196851808).

Almost surely, 2^21688981321 is an apocalyptic number.

It is an amenable number.

21688981321 is a deficient number, since it is larger than the sum of its proper divisors (3098425911).

21688981321 is an equidigital number, since it uses as much as digits as its factorization.

21688981321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3098425910.

The product of its digits is 331776, while the sum is 49.

The spelling of 21688981321 in words is "twenty-one billion, six hundred eighty-eight million, nine hundred eighty-one thousand, three hundred twenty-one".