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Pick out the term that breaks the pattern: 1, 3, 9, 31, 128, 651

Competition practiceNumber Series

A9
B31
C128
D651

Step-by-Step Solution

Pattern is

\times 1 + 2, \times 2 + 3, \times 3 + 4, \times 4 + 5, \times 5 + 6

, giving 1, 3, 9, 31, 129, 651; so 128 should be 129.

Answer: C) 128

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