Which number does not belong in the series below? 2, 5, 10, 17, 26, 37, 50, 64, 66 A. 17 B. 37 C. 64 D. 26

GATE 2014 · General Aptitude · Number Series · easy

Answer: 64 (should be 65 = 8^2 + 1)

1. Identify the rule by computing consecutive differences: Differences: 5-2=3, 10-5=5, 17-10=7, 26-17=9, 37-26=11, 50-37=13. These are consecutive odd numbers 3, 5, 7, 9, 11, 13, confirming a_n = n^2 + 1.
2. Find the outlier: Expected 8th term = 8^2 + 1 = 65. Given value = 64. Difference 64 - 50 = 14 (should be 15). So 64 does not belong — the correct value is 65.