13. If ∣∣∣∣∣a2(a+1)2(a−1)2b2(b+1)2(b−1)2c2(c+1)2(c−1)2∣∣∣∣∣=k∣∣∣∣a2a1b2b1c2c1∣∣∣∣|a2b2c2(a+1)2(b+1)2(c+1)2(a−1)2(b−1)2(c−1)2|=k|a2b2c2abc111| then the value of kk is

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