21919321 has 2 divisors, whose sum is σ = 21919322. Its totient is φ = 21919320.

The previous prime is 21919319. The next prime is 21919349. The reversal of 21919321 is 12391912.

It is an a-pointer prime, because the next prime (21919349) can be obtained adding 21919321 to its sum of digits (28).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20793600 + 1125721 = 4560^2 + 1061^2 .

It is a cyclic number.

It is not a de Polignac number, because 21919321 - 2¹ = 21919319 is a prime.

Together with 21919319, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21919321.

It is not a weakly prime, because it can be changed into another prime (21919361) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10959660 + 10959661.

It is an arithmetic number, because the mean of its divisors is an integer number (10959661).

Almost surely, 2^21919321 is an apocalyptic number.

It is an amenable number.

21919321 is a deficient number, since it is larger than the sum of its proper divisors (1).

21919321 is an equidigital number, since it uses as much as digits as its factorization.

21919321 is an evil number, because the sum of its binary digits is even.

The product of its digits is 972, while the sum is 28.

The square root of 21919321 is about 4681.8074501201. The cubic root of 21919321 is about 279.8609896711.

The spelling of 21919321 in words is "twenty-one million, nine hundred nineteen thousand, three hundred twenty-one".