
    In a student performance tracking system that uses octagonal patterns to visualize academic progress at key checkpoints, develop a function that calculates the size of the visual pattern at the nth checkpoint. The pattern grows systematically according to the octagonal number sequence, where each subsequent checkpoint's pattern is formed by adding an increasing number of data points around the previous octagon's perimeter.
    

    
def is_octagonal(n):
    """
    In a student performance tracking system that uses octagonal patterns to visualize academic progress at key checkpoints, develop a function that calculates the size of the visual pattern at the nth checkpoint. The pattern grows systematically according to the octagonal number sequence, where each subsequent checkpoint's pattern is formed by adding an increasing number of data points around the previous octagon's perimeter.
    

    """
def is_octagonal(n):
    """
    In a student performance tracking system that uses octagonal patterns to visualize academic progress at key checkpoints, develop a function that calculates the size of the visual pattern at the nth checkpoint. The pattern grows systematically according to the octagonal number sequence, where each subsequent checkpoint's pattern is formed by adding an increasing number of data points around the previous octagon's perimeter.
    

    """
    return 3 * n * n - 2 * n