Chapter 1: Q21E (page 49)
How many integers modulo have inverses?
Short Answer
The number of integers coprime to are 1210
/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none}
Learning Materials
Features
Discover
Chapter 1: Q21E (page 49)
How many integers modulo have inverses?
The number of integers coprime to are 1210
All the tools & learning materials you need for study success - in one app.
Get started for free
On page 38, we claimed that since about a fraction of n-bit numbers are prime, on average it is sufficient to draw random n -bit numbers before hitting a prime. We now justify this rigorously. Suppose a particular coin has a probability p of coming up heads. How many times must you toss it, on average, before it comes up heads? (Hint: Method 1: start by showing that the correct expression is . Method 2: if E is the average number of coin tosses, show that ).
Determine necessary and sufficient conditions on so that the following holds: for any if , then .
Show that any binary integer is at most four times as long as the corresponding decimal integer. For very large numbers, what is the ratio of these two lengths, approximately?
1.36. Square roots. In this problem, we'll see that it is easy to compute square roots modulo a prime pwith .
(a) Suppose . Show that is an integer.
(b) We say x is a square root of a modulo p if . Show that if and if a has a square root modulo p, then is such a square root.
Prove or disprove: If a has an inverse modulo b, then b has an inverse modulo a.
What do you think about this solution?
We value your feedback to improve our textbook solutions.