#include <stdio.h>
//練習問題E
int tri(int n){
	int a,b=1,c=0,d=0;
	for(int i=3;i<=n;i++){
		a=b+c+d;
		d=c;
		c=b;
		b=a;
	}return a;
}
 
 
 
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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