Diagram 1 (6)
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Diagram 2 (12)
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Diagram 3 (20)
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Diagram 4 (30)
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The general pattern is n(n+1) where n is the number of asterisk pairs on the last row and n-1 is the diagram number.
So, Diagram 10 has 11 pairs of asterisks, so the total number is 11*12=132.