21643331 has 2 divisors, whose sum is σ = 21643332. Its totient is φ = 21643330.

The previous prime is 21643313. The next prime is 21643333. The reversal of 21643331 is 13334612.

Together with previous prime (21643313) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21643331 - 2⁶ = 21643267 is a prime.

It is a super-2 number, since 2×21643331² = 936867553551122, which contains 22 as substring.

Together with 21643333, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21643297 and 21643306.

It is not a weakly prime, because it can be changed into another prime (21643333) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10821665 + 10821666.

It is an arithmetic number, because the mean of its divisors is an integer number (10821666).

Almost surely, 2^21643331 is an apocalyptic number.

21643331 is a deficient number, since it is larger than the sum of its proper divisors (1).

21643331 is an equidigital number, since it uses as much as digits as its factorization.

21643331 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1296, while the sum is 23.

The square root of 21643331 is about 4652.2393532577. The cubic root of 21643331 is about 278.6814321887.

Adding to 21643331 its reverse (13334612), we get a palindrome (34977943).

The spelling of 21643331 in words is "twenty-one million, six hundred forty-three thousand, three hundred thirty-one".