#include <stdio.h>
//a{n} = 2a{n-1} + a{n-2}, a{1}=2, a{2}=3(再帰なし版)
//第5回課題1
int main(void) {
int n = 4;
int a, b = 3, c = 2;
for(int i =3 ; i <= n; i++){
a = 2*b + c;
c = b;
b = a;
}
return 0;
}
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