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    • Read instructions carefully.
    • Its not an issue
    The sum of the digits should be a multiple of a perfect square number.
    # 4 is a perfect square number and a multiple of 4 + 3 + 1 = 8.
    
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    In the basic tests, 431 is included as one of the possible special primes, even though it does not meet the condition of its digit sum being a perfect square.