sieve_phi.cpp

#include<stdio.h>

int phi[1000006], mark[1000006];

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

    for(i=1; i<=n; i++) phi[i] = i;

    phi[1] = 1;
    mark[1] = 1;

    for(i=2; i<=n; i++)
        if(!mark[i])
            for(j=i; j<=n; j+=i)
            {
                mark[j] = 1;
                phi[j] = phi[j] / i * (i-1);
            }
}

int main()
{
    int n = 30, i;

    seivephi(n);

    printf("   i: ");
    for(i=1; i<=n; i++)
        printf("%3d%c", i, i<n?' ':'\n');

    printf(" phi: ");
    for(i=1; i<=n; i++)
        printf("%3d%c", phi[i], i<n?' ':'\n');

    printf("mark: ");
    for(i=1; i<=n; i++)
        printf("%3d%c", mark[i], i<n?' ':'\n');

    return 0;
}