#include <stdio.h>
//練習問題G
 
int main(void){
   int a, b=2, c=1,n=3;
    int i;
     for(i=3;i<=n;i++){
    	a=b+2*c-2*i;
    	b=a;
    	c=b;
    }
    printf("数列anについて, n=%dのときの値は%d\n", n
,a
); 	return 0;
}
 
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