What should come in place of question mark (?) in the given number series ?
5 9 35 209 ? 16709

Options

A. 1711
B. 1574
C. 1627
D. 1671

Answer

To solve the number series 5, 9, 35, 209, ?, 16709, we need to identify the pattern in the series.

### Step-by-Step Solution:

1. **Identify the pattern between the numbers:**
- Start with the first two numbers: 5 and 9.
- To go from 5 to 9, we can multiply 5 by 2 and then subtract 1:
\[ 5 \times 2 = 10 \quad \text{and} \quad 10 - 1 = 9 \]

2. **Continue to the next pair:**
- Now, from 9 to 35:
- Multiply 9 by 4 and then subtract 1:
\[ 9 \times 4 = 36 \quad \text{and} \quad 36 - 1 = 35 \]

3. **Next, from 35 to 209:**
- Multiply 35 by 6 and then subtract 1:
\[ 35 \times 6 = 210 \quad \text{and} \quad 210 - 1 = 209 \]

4. **Now, find the missing number after 209:**
- Following the established pattern, we should multiply 209 by 8 and then subtract 1:
\[ 209 \times 8 = 1672 \quad \text{and} \quad 1672 - 1 = 1671 \]

5. **Finally, verify the last number in the series:**
- To confirm, we check the transition from 1671 to 16709:
- Multiply 1671 by 10 and then subtract 1:
\[ 1671 \times 10 = 16710 \quad \text{and} \quad 16710 - 1 = 16709 \]

### Conclusion:
The number that should come in place of the question mark (?) is **1671**.