The following number series has one wrong term. Find the wrong term. 3, 4, 7,…

In this number-series pattern, each term is formed by adding the next consecutive odd number (1, 3, 5, 7, 9, 11, ...) to the term before it. To find the wrong term, generate the expected value at each step and compare it with the number actually written in the series — the value that does not match its expected term is the wrong one.

1. 3 + 1 = 4

2. 4 + 3 = 7

3. 7 + 5 = 12

4. 12 + 7 = 19

5. 19 + 9 = 28 (expected), but the series shows 35 instead

6. 28 + 11 = 39, which matches the series's actual last term

Since 19 + 9 should give 28, not 35, the term 35 does not follow the rule that generates every other number in this series.

Cross-check with the closed-form rule: the sum of the first (k − 1) consecutive odd numbers equals (k − 1)2, so the k-th term equals 3 + (k − 1)2. This gives the terms 3, 4, 7, 12, 19, 28, 39 for positions 1 to 7. Comparing with the given series 3, 4, 7, 12, 19, 35, 39 shows a mismatch only at the sixth position (35 instead of 28), while the seventh term, 39, matches exactly — confirming that 35 is the wrong term.

Hence, 35 is the wrong term.