Largest integer that can be represented in a n-bit integer word

To find the largest integer in base-10 that can be represented in an n-bit integer word, let’s do this inductively.

  • If you have 3 bit-word, the highest number is (111) of base-2 which is 7 (1*2^2+1*2^1+1*2^0) of base-10,
  • If you have 4 bit-word, the highest number is (1111) of base-2 which is 15 (1*2^3+1*2^2+1*2^1+1*2^0) of base-10,
  • if you have 5 bit-word, the highest number is (11111) of base-2 which is 31 (1*2^4+1*2^3+1*2^2+1*2^1+1*2^0) of base-10. 

There is a trend here: 3 bit-word stores a maximum number of 7 (2^3-1), 4-bit word stores a maximum of 15 (2^4-1), 5 bit-word store a maximum number of 31 (2^5-1), and so on.   This means that the maximum number stored in n-bit word stores a maximum number of 2^n-1. 

We can derive the maximum number by knowing that the maximum base-10 number in a n-bit word is the summation series:
This is a geometric progression series.  The formula for the sum of a geometric series
        a+ar+ar^2+…+a*r^n =a*(1-r^(n+1))/(1-r), r ≠ 1,
       1*2^(n-1)+1*2^(n-2)+………+1×2^0=1*(1-2^(n))/(1-2)=2^n-1 _____________________________________________________________

This post is brought to you by Holistic Numerical Methods: Numerical Methods for the STEM undergraduate at, the textbook on Numerical Methods with Applications available from the lulu storefront, the textbook on Introduction to Programming Concepts Using MATLAB, and the YouTube video lectures available at  Subscribe to the blog via a reader or email to stay updated with this blog. Let the information follow you.