21931321 has 2 divisors, whose sum is σ = 21931322. Its totient is φ = 21931320.

The previous prime is 21931313. The next prime is 21931331. The reversal of 21931321 is 12313912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17139600 + 4791721 = 4140^2 + 2189^2 .

It is a cyclic number.

It is not a de Polignac number, because 21931321 - 2³ = 21931313 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21931292 and 21931301.

It is not a weakly prime, because it can be changed into another prime (21931331) 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 as a sum of consecutive naturals, namely, 10965660 + 10965661.

It is an arithmetic number, because the mean of its divisors is an integer number (10965661).

Almost surely, 2^21931321 is an apocalyptic number.

It is an amenable number.

21931321 is a deficient number, since it is larger than the sum of its proper divisors (1).

21931321 is an equidigital number, since it uses as much as digits as its factorization.

21931321 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 324, while the sum is 22.

The square root of 21931321 is about 4683.0888311028. The cubic root of 21931321 is about 279.9120514597.

The spelling of 21931321 in words is "twenty-one million, nine hundred thirty-one thousand, three hundred twenty-one".