Find the wrong term in the number series: 2, 8, 32, 148, 765, 4626, 32431. Exactly one term violates a consistent pattern; identify the incorrect term.

Difficulty: Medium

Correct Answer: 32

Explanation:


Introduction / Context:
This is a wrong-term detection problem in a number series. We must discover a single, clean rule that fits all positions except one, and then mark the violating term.


Given Data / Assumptions:

  • Series: 2, 8, 32, 148, 765, 4626, 32431.
  • Index n starts at 1 for the first step (from 2 to 8).
  • Look for multiplicative growth with a small additive adjustment.


Concept / Approach:
A compact pattern that nearly fits is: a(n+1) = a(n) * (n+1) + (n+1)^2. We verify each transition and isolate any mismatch.


Step-by-Step Solution:

2 → 8: 2*2 + 2^2 = 4 + 4 = 8 ✔8 → 32: 8*3 + 3^2 = 24 + 9 = 33 ✖ (given 32)32 → 148: 32*4 + 4^2 = 128 + 16 = 144 ✖ (given 148)148 → 765: 148*5 + 25 = 740 + 25 = 765 ✔765 → 4626: 765*6 + 36 = 4590 + 36 = 4626 ✔4626 → 32431: 4626*7 + 49 = 32382 + 49 = 32431 ✔


Verification / Alternative check:
If the 3rd term were 33 instead of 32, then 33*4 + 16 = 148 (exact). Thus a single earlier slip (32 vs 33) explains both mismatches and restores a perfect rule for the tail.


Why Other Options Are Wrong:
Terms 8, 148, 765 all become consistent once the 3rd term is corrected from 32→33; they are not the primary error.


Common Pitfalls:
Blaming a later term when an earlier off-by-one causes downstream wobble. Always check if fixing one term repairs later transitions.


Final Answer:
32 is the lone wrong term under a(n+1) = a(n)*(n+1) + (n+1)^2.

More Questions from Number Series

Discussion & Comments

No comments yet. Be the first to comment!
Join Discussion