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## 762. Prime Number of Set Bits in Binary Representation (Easy)

Given two integers `L` and `R`, find the count of numbers in the range `[L, R]` (inclusive) having a prime number of set bits in their binary representation.

(Recall that the number of set bits an integer has is the number of `1`s present when written in binary. For example, `21` written in binary is `10101` which has 3 set bits. Also, 1 is not a prime.)

Example 1:

```Input: L = 6, R = 10
Output: 4
Explanation:
6 -> 110 (2 set bits, 2 is prime)
7 -> 111 (3 set bits, 3 is prime)
9 -> 1001 (2 set bits , 2 is prime)
10->1010 (2 set bits , 2 is prime)
```

Example 2:

```Input: L = 10, R = 15
Output: 5
Explanation:
10 -> 1010 (2 set bits, 2 is prime)
11 -> 1011 (3 set bits, 3 is prime)
12 -> 1100 (2 set bits, 2 is prime)
13 -> 1101 (3 set bits, 3 is prime)
14 -> 1110 (3 set bits, 3 is prime)
15 -> 1111 (4 set bits, 4 is not prime)
```

Note:

1. `L, R` will be integers `L <= R` in the range `[1, 10^6]`.
2. `R - L` will be at most 10000.

### Similar Questions

1. Number of 1 Bits (Easy)

### Hints

Hint 1 Write a helper function to count the number of set bits in a number, then check whether the number of set bits is 2, 3, 5, 7, 11, 13, 17 or 19.
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