21647321 has 2 divisors, whose sum is σ = 21647322. Its totient is φ = 21647320.

The previous prime is 21647299. The next prime is 21647323. The reversal of 21647321 is 12374612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19456921 + 2190400 = 4411^2 + 1480^2 .

It is a cyclic number.

It is not a de Polignac number, because 21647321 - 2²² = 17453017 is a prime.

Together with 21647323, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21647323) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10823660 + 10823661.

It is an arithmetic number, because the mean of its divisors is an integer number (10823661).

Almost surely, 2^21647321 is an apocalyptic number.

It is an amenable number.

21647321 is a deficient number, since it is larger than the sum of its proper divisors (1).

21647321 is an equidigital number, since it uses as much as digits as its factorization.

21647321 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2016, while the sum is 26.

The square root of 21647321 is about 4652.6681592394. The cubic root of 21647321 is about 278.6985563334.

The spelling of 21647321 in words is "twenty-one million, six hundred forty-seven thousand, three hundred twenty-one".