Discussion

Find out the wrong number in the series 7, 8, 18, 57, 228, 1165, 6996

Answer: D

Each step multiplies by an increasing integer and adds the same integer.

\[ 7 \times 1 + 1 = 8 \quad\checkmark \]

\[ 8 \times 2 + 2 = 18 \quad\checkmark \]

\[ 18 \times 3 + 3 = 57 \quad\checkmark \]

\[ 57 \times 4 + 4 = 232 \quad\text{but the series shows } 228 \]

So 228 is wrong. The rest confirm 232: \( 232 \times 5 + 5 = 1165 \) and \( 1165 \times 6 + 6 = 6996 \).

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