21497321 has 2 divisors, whose sum is σ = 21497322. Its totient is φ = 21497320.

The previous prime is 21497317. The next prime is 21497339. The reversal of 21497321 is 12379412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15713296 + 5784025 = 3964^2 + 2405^2 .

It is a cyclic number.

It is not a de Polignac number, because 21497321 - 2² = 21497317 is a prime.

It is not a weakly prime, because it can be changed into another prime (21497351) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10748660 + 10748661.

It is an arithmetic number, because the mean of its divisors is an integer number (10748661).

Almost surely, 2^21497321 is an apocalyptic number.

It is an amenable number.

21497321 is a deficient number, since it is larger than the sum of its proper divisors (1).

21497321 is an equidigital number, since it uses as much as digits as its factorization.

21497321 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3024, while the sum is 29.

The square root of 21497321 is about 4636.5203547488. The cubic root of 21497321 is about 278.0533384535.

The spelling of 21497321 in words is "twenty-one million, four hundred ninety-seven thousand, three hundred twenty-one".