Math Problem Statement
Question 3 For n ∈ N 0 n∈N 0 let w ( n ) w(n) denote the number of 1 1s in the binary representation of n n. For example, w ( 9 )
2 w(9)=2, since $9$ is 1001 1001 in binary. Try to find a closed formula for g ( n ) g(n) in terms of n n and w ( n ) w(n). If you succeed, the following question will be very easy.
Let n
10000000000000011 n=10000000000000011 in binary notation. What is g ( n ) g(n)? Write your answer in binary!
0 / 1 point Incorrect 4. Question 4 Let n
1152921504606846987 n=1152921504606846987. If we compute ( n k ) m o d 2 ( k n )mod2 for k
0 … 7 k=0…7, which sequence do we get?
Write your answer as a simple 0/1 string. For example, if your sequence is ( 1 , 0 , 1 , 0 , 1 , 0 , 1 , 0 ) (1,0,1,0,1,0,1,0), answer 10101010 10101010.
Solution
Let's break down and solve the questions one by one.
Question 3: Finding
Given:
- denotes the number of 1s in the binary representation of .
We need to find a closed formula for in terms of and .
Let's analyze the problem by first understanding . In many problems involving binary representations, a common pattern is counting specific bit configurations or analyzing parity.
For example, consider the function . This function would combine with the number of 1s in its binary form. Let's now try to apply this and see what happens when we use a specific .
Given (in binary):
-
Convert to decimal:
-
Calculate , the number of 1s in the binary representation:
-
Let's assume as a possible formula. Substituting the values:
-
Convert back to binary:
This would be the result, but it does not necessarily match any specific answer format expected. Thus, let's revisit the definition of .
Understanding
Since we are asked to relate with , consider another simpler function like . This will likely involve a modular reduction or additional operation. Let’s try to simplify:
Question 4: Sequence from Binomial Coefficients Modulo 2
Given :
We need to calculate for .
Steps:
-
Convert to binary:
-
For each , determine :
Use Lucas' theorem, which states: where and are the binary digits of and , respectively.
-
The sequence for to corresponds to the binary digits of restricted to the first 3 digits (since the binomial coefficient of any bit higher than would cancel out):
- For , .
- For , (if the least significant bit is 1).
- Continue for all to .
The sequence is therefore:
This sequence comes from the fact that has 1s in the first and second least significant positions.
Summary:
- Question 3: The binary result was an attempt based on a function with the hypothesis that could be incorrect as it does not yield standard expected results.
- Question 4: The correct answer sequence is
11000000
.
Would you like to go through the steps in more detail or explore further examples?
Relative Questions:
- How can Lucas' theorem be generalized for other moduli?
- What are the properties of binary representations when considering bit manipulation?
- What would be if we modified the problem to use different weights?
- What happens if is a very large number, like in the case of very dense binary numbers?
- How does one efficiently compute large binomial coefficients modulo small primes?
Tip: Always try decomposing complex binary or modular problems using smaller, simpler examples to verify your hypotheses.
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Math Problem Analysis
Mathematical Concepts
Number Theory
Binary Representation
Combinatorics
Formulas
w(n): Number of 1s in the binary representation of n
g(n): Hypothetical function involving binary operations
Theorems
Lucas' Theorem
Suitable Grade Level
Grades 11-12
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