Multiple choice

In the following number series only one number is wrong. Find out the wrong number? 6, 15, 35, 63, 143, 221, 323

  1. 35

  2. 63

  3. 15

  4. 323

  5. 221
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Check differences: 6→15 (+9), 15→35 (+20), 35→63 (+28), 63→143 (+80), 143→221 (+78), 221→323 (+102). This is irregular. Try alternate pattern or factor-based: 6=2²+2, 15=4²-1, 35=6²-1, 63=8²-1. Pattern: even squares plus/minus constant. Following this: 10²-1=99 (not 143), so 143 breaks it. Or: 6=2×3, 15=3×5, 35=5×7, 63=7×9, next should be 9×11=99 (not 143). So 63 is wrong. Answer 63 is correct.

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