
Shortcut Trick
Identify numbers in the range 400 to 430 that are not divisible by 2, 3, 5, 7, 11, 13, 17, or 19.
Numbers to check: 401, 403, 407, 409, 413, 419, 421, 427, 429.
Eliminate: 403 (13×31), 407 (11×37), 413 (7×59), 427 (7×61), 429 (3×143).
Remaining Prime Numbers: 401, 409, 419, 421.
∴ The correct answer is 4.

Alternate Method
Given: Range of numbers between 400 and 430.
Method: To check if a number n is prime, test divisibility by all primes ≤ √n. Here, √430 ≈ 20.7, so test primes 2, 3, 5, 7, 11, 13, 17, 19.
⇒ 401: Not divisible by 2, 3, 5, 7, 11, 13, 17, 19 → Prime
⇒ 403: 13 × 31 = 403 → Not Prime
⇒ 407: 11 × 37 = 407 → Not Prime
⇒ 409: Not divisible by 2, 3, 5, 7, 11, 13, 17, 19 → Prime
⇒ 419: Not divisible by 2, 3, 5, 7, 11, 13, 17, 19 → Prime
⇒ 421: Not divisible by 2, 3, 5, 7, 11, 13, 17, 19 → Prime
⇒ List of primes: {401, 409, 419, 421}
⇒ Total count = 4
∴ The correct answer is 4.

Additional Information
Definition of Prime Numbers
A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself.
Primality Test Rule
To check if N is prime, divide N by all prime numbers less than or equal to √N. If none divide N, then N is prime.
Twin Primes
Pairs of prime numbers that have a difference of 2 (e.g., 419 and 421 are twin primes).