#include <stdio.h>
//練習問題E
int tri(int a){
	if(a == 0){
		return 0;
	}else if(a == 1){
		return 0;
	}else if(a == 2){
		return 1;
	}else{
		return tri(a-1)+tri(a-2)+tri(a-3);
	}
}
 
 
 
int main(void) {
	int n = 7;
    printf("数列Tnについて, n=%dのときの値は%d\n", n
, tri
(n
)); 	return 0;
}
 
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