input: Write a function to print out the first n prime numbers using the Sieve of Eratosthenes algorithm. The function should return a list of these prime numbers. If n is less than 1, return an empty list.
  
  def first_n_primes(n):
      if n < 1:
          return []
      max_num = 1000  # Assuming a reasonable upper limit for finding primes
      primes = [True] * (max_num + 1)
      primes[0] = primes[1] = False
      for i in range(2, int(max_num**0.5) + 1):
          if primes[i]:
              for j in range(i * i, max_num + 1, i):
                  primes[j] = False
      prime_numbers = [i for i, is_prime in enumerate(primes) if is_prime]
      return prime_numbers[:n]
  
  assert first_n_primes(0) == []
  assert first_n_primes(1) == [2]
  assert first_n_primes(5) == [2, 3, 5, 7, 11]
  assert first_n_primes(10) == [2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
  assert first_n_primes(20) == [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71]
output: def first_n_primes(n):
      if n < 1:
          return []
      max_num = 1000  # Assuming a reasonable upper limit for finding primes
      primes = [True] * (max_num + 1)
      primes[0] = primes[1] = False
      for i in range(2, int(max_num**0.5) + 1):
          if primes[i]:
              for j in range(i * i, max_num + 1, i):
                  primes[j] = False
      prime_numbers = [i for i, is_prime in enumerate(primes) if is_prime]
      return prime_numbers[:n]