#include <stdio.h>
//練習問題E
int tri(int n) {
 
if(n==0)
{
	return 0;
}
 
else if(n==1)
{
	return 0;
}
 
else if(n==2)
{
	return 1;
}
 
else
{
	return tri(n-1)+tri(n-2)+tri(n-3);
}
 
}
 
int main(void) {
	int n = 7;
	tri(n);
    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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