#include <stdio.h>

//a{n}=2a_{n-1}+3, a{0}=-2(再帰無し版)
int main(void) {
    int n,an;
    int i;

    n = 4;
    an = -2;

    for(i = 1; i <= n; i++){
        an = 2 * an + 3;
    }

    printf("数列anの%d番目の値は%d\n", n, an);
    return 0;
}