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Question

What should come at the place of question mark? : 31, 63, 127, 255, 511, ?

This question was previously asked in
SSC CGL 2025 Tier 1 Question Paper (25-Sep-2025) (Shift 3)
The correct answer is
1023

Sequence Pattern Identification

The question presents a sequence: 31, 63, 127, 255, 511, ?

We need to identify the pattern governing this sequence to find the missing term.

Analyzing the Sequence

Let's examine the relationship between consecutive terms or the structure of each term:

  • The first term is 31.
  • The second term is 63.
  • The third term is 127.
  • The fourth term is 255.
  • The fifth term is 511.

Finding the Mathematical Pattern

Observe the terms in relation to powers of 2:

  • $31 = 32 - 1 = 2^5 - 1$
  • $63 = 64 - 1 = 2^6 - 1$
  • $127 = 128 - 1 = 2^7 - 1$
  • $255 = 256 - 1 = 2^8 - 1$
  • $511 = 512 - 1 = 2^9 - 1$

The pattern is $2^n - 1$, where n starts from 5 and increases by 1 for each subsequent term.

Calculating the Missing Term

Following the identified pattern, the next term should correspond to $n=10$.

The calculation is:

$2^{10} - 1 = 1024 - 1 = 1023$

Conclusion

Therefore, the number that should come at the place of the question mark is 1023.

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