#include <stdio.h>
//a{n}=2a_{n-1}+3, a{0}=-2(再帰無し版)
int main(void) {
    int n,an;
    n = 4;
    an = -2;
    for(int i = 0;i < n;i++){
    	an = 2*an + 3;
    }


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