21724321 has 2 divisors, whose sum is σ = 21724322. Its totient is φ = 21724320.

The previous prime is 21724309. The next prime is 21724333. The reversal of 21724321 is 12342712.

It is a balanced prime because it is at equal distance from previous prime (21724309) and next prime (21724333).

It can be written as a sum of positive squares in only one way, i.e., 20802721 + 921600 = 4561^2 + 960^2 .

It is a cyclic number.

It is not a de Polignac number, because 21724321 - 2⁷ = 21724193 is a prime.

It is a super-2 number, since 2×21724321² = 943892245822082, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21724292 and 21724301.

It is not a weakly prime, because it can be changed into another prime (21724361) 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, 10862160 + 10862161.

It is an arithmetic number, because the mean of its divisors is an integer number (10862161).

Almost surely, 2^21724321 is an apocalyptic number.

It is an amenable number.

21724321 is a deficient number, since it is larger than the sum of its proper divisors (1).

21724321 is an equidigital number, since it uses as much as digits as its factorization.

21724321 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 672, while the sum is 22.

The square root of 21724321 is about 4660.9356356852. The cubic root of 21724321 is about 279.0286109498.

The spelling of 21724321 in words is "twenty-one million, seven hundred twenty-four thousand, three hundred twenty-one".