Problema 4 :
#include <stdio.h>
#include <conio.h>

int cmmdc(int a, int b) {
	int r;
	r = a%b;
	while (r != 0) {
		a = b;
		b = r;
		r = a%b;
	}
	return b;
}

void main() {
	int n, i, j;

	printf("n=");
	scanf_s("%d", &n);
	while (n < 2) {
		printf("n trebuie sa fie mai mare ca 1: ");
		scanf_s("%d", &n);
	}
	printf("\nTabela de adunare din Z%d este:\n+ ", n);
	for (i = 0; i < n; i++)
		printf("%d ", i);
	printf("\n");
	for (i = 0; i < n; i++) {
		printf("%d ", i);
		for (j = 0; j < n; j++) {
			printf("%d ", (i + j) % n);
		}
		printf("\n");
	}

	printf("\nTabela de inmultire din Z%d este:\n* ", n);
	for (i = 0; i < n; i++)
		printf("%d ", i);
	printf("\n");
	for (i = 0; i < n; i++) {
		printf("%d ", i);
		for (j = 0; j < n; j++) {
			printf("%d ", (i*j) % n);
		}
		printf("\n");
	}

	printf("\nU(Z%d) = { ", n);
	for (i = 0; i < n; i++)
		if (cmmdc(i, n) == 1)
			printf("%d ", i);
	printf("}");

	printf("\nD(Z%d) = { ", n);
	for (i = 0; i < n; i++)
		if (cmmdc(i, n) != 1)
			printf("%d ", i);
	printf("}");

	int f = 2, produs = 1, el = n;
	while (n != 1) {
		if (n%f == 0)
			produs = produs*f;
		while (n%f == 0)
			n = n / f;
		f++;
	}
	printf("\nD(N%d) = { 0 ", el);
	int aux = 1;
	while (produs*aux < el) {
		printf("%d ", produs*aux);
		aux++;
	}
	printf("}");
	_getch();
}
Problema 3:
#include <stdio.h>
#include <conio.h>
#include <math.h>

int cmmdc(int a, int b) {
	int r;
	r = a%b;
	while (r != 0) {
		a = b;
		b = r;
		r = a%b;
	}
	return b;
}

int cmmmc(int a, int b) {
	return (a*b) / cmmdc(a, b);
}

int prim(int a) {
	int ok = 1;

	for (int d = 2; d <= sqrt(a); d++)
		if (a%d == 0)
			ok = 0;
	return ok;
}

void main() {
	int n, d[100], nd, i, j;

	printf("Introduceti n=");
	scanf_s("%d", &n);
	nd = 0;
	for (i = 1; i <= n; i++)
		if (n%i == 0)
			d[nd++] = i;
	printf("Divizorii lui %d sunt: ", n);
	for (i = 0; i < nd; i++)
		printf("%d ", d[i]);

	printf("\nTabela corespunzatoare a^b este: \n");
	for (i = 0; i < nd; i++) {
		for (j = 0; j < nd; j++) {
			printf("%d ", cmmdc(d[i], d[j]));
		}
		printf("\n");
	}

	printf("\nTabela corespunzatoare avb este: \n");
	for (i = 0; i < nd; i++) {
		for (j = 0; j < nd; j++) {
			printf("%d ", cmmmc(d[i], d[j]));
		}
		printf("\n");
	}

	int ok = 1;
	for (i = 2; i <= sqrt(n); i++) {
		if ((prim(i)==1) && (cmmdc(n, i*i) != 1))
			ok = 0;
	}
	if (ok)
		printf("\n%d este liber de patrate.", n);
	else
		printf("\n%d nu este liber de patrate.", n);
	_getch();
}