# EVOLVE-BLOCK-START
import numpy as np


def circle_packing21() -> np.ndarray:
    """
    Places 21 non-overlapping circles inside a rectangle of perimeter 4 in order to maximize the sum of their radii.

    Returns:
        circles: np.array of shape (21,3), where the i-th row (x,y,r) stores the (x,y) coordinates of the i-th circle of radius r.
    """
    n = 21
    circles = np.zeros((n, 3))

    return circles


# EVOLVE-BLOCK-END

if __name__ == "__main__":
    circles = circle_packing21()
    print(f"Radii sum: {np.sum(circles[:,-1])}")