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Exercise 17.8 Find all positive integers n for which o(n) = 60. Whenever a mathematician asks...
Problem 2. Find (with proof) all positive integers n that have an odd number of positive divisors (for example 6 has 4 positive divisors 1,2,3,6).
1. (Integers: primes, divisibility, parity.) (a) Let n be a positive integer. Prove that two numbers na +3n+6 and n2 + 2n +7 cannot be prime at the same time. (b) Find 15261527863698656776712345678%5 without using a calculator. (c) Let a be an integer number. Suppose a%2 = 1. Find all possible values of (4a +1)%6. 2. (Integers: %, =) (a) Suppose a, b, n are integer numbers and n > 0. Prove that (a+b)%n = (a%n +B%n)%n. (b) Let a,...
Exercise 2. Let φ denote the Euler totient function. (i) Prove that for all positive integers m and n, if m,n are relatively prime (coprime), then φ(mn-o(m)o(n) (ii) Is the converse true? Prove or provide a counter-example.
8. Define (n) to be the number of positive integers less than n and n. That is, (n) = {x e Z; 1 < x< n and gcd(x, n) = 1}|. Notice that U (n) |= ¢(n). For example U( 10) = {1, 3,7, 9} and therefore (10)= 4. It is well known that (n) is multiplicative. That is, if m, n are (mn) (m)¢(n). In general, (p") p" -p Also it's well known that there are relatively prime, then...
1 For each of the following pairs of numbers a and b, calculate and find integers r and s such ged (a; b) by Eucledian algorithm that gcd(a; b) = ra + sb. ia= 203, b-91 ii a = 21, b=8 2 Prove that for n 2 1,2+2+2+2* +...+2 -2n+1 -2 3 Prove that Vn 2 1,8" -3 is divisible by 5. 4 Prove that + n(n+1) = nnīYn E N where N is the set of all positive integers....
Given an array A[1..n] of positive integers and given a number x, find if any two numbers in this array sum upto x. That is, are there i,j such that A[i]+A[j] = x? Give an O(nlogn) algorithm for this. Suppose now that A was already sorted, can you obtain O(n) algorithm?
(on this page, A, B, C, D are all positive integers and A/B <C/D.) We saw in the previous assignment that CA CB - AD 1 DB=BD ? BD (The numerator must be an integer, and since the two fractions are unequal, it can't be 0.) In other words, "the closest two unequal rational numbers and can be is BD" (9.1) A sort of average of two fractions: . Show that <A+O- We gave an intuitive explanation of this in...
8. Consider the following algorithm, which finds the sum of all of the integers in a list procedure sum(n: positive integer, a1, a2,..., an : integers) for i: 1 to n return S (a) Suppose the value for n is 4 and the elements of the list are 3, 5,-2,4. List assigned to s as the procedure is executed. (You can list the the values that are values assigned to all variables if you wish) b) When a list of...
13. (i) For each of the following equations, find all the natural numbers n that satisfy it (a) φ(n)-4 (b) o(n) 6 (c) ф(n) 8 (d) φ(n) = 10 (ii) Prove or disprove: (a) For every natural number k, there are only finitely many natural num- bers n such that ф(n)-k (b) For every integer n > 2, there are at least two distinction integers that are invertible modulo n (c) For every integers a, b,n with n > 1...
6.32 Theorem. If k and n are natural numbers with (k, d(n)) =I, then there exist positive integers u and v satisfving ku=(n)u The previous theorem not only asserts that an appropriate exponent is always availahle, but it also tells us how to find it. The numbers u and are solutions lo a lincar Diophantine cquation just like those we studied in Chapter 6.33 Exercisc. Use your observations so far to find solutions to the follow ing congruences. Be sure...