21956321 has 2 divisors, whose sum is σ = 21956322. Its totient is φ = 21956320.

The previous prime is 21956317. The next prime is 21956323. The reversal of 21956321 is 12365912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21669025 + 287296 = 4655^2 + 536^2 .

It is a cyclic number.

It is not a de Polignac number, because 21956321 - 2² = 21956317 is a prime.

It is a Sophie Germain prime.

Together with 21956323, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21956323) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10978160 + 10978161.

It is an arithmetic number, because the mean of its divisors is an integer number (10978161).

Almost surely, 2^21956321 is an apocalyptic number.

It is an amenable number.

21956321 is a deficient number, since it is larger than the sum of its proper divisors (1).

21956321 is an equidigital number, since it uses as much as digits as its factorization.

21956321 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 29.

The square root of 21956321 is about 4685.7572493675. The cubic root of 21956321 is about 280.0183703934.

The spelling of 21956321 in words is "twenty-one million, nine hundred fifty-six thousand, three hundred twenty-one".