#include <stdio.h>
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;
}
printf("数列のa%dの値は%d\n", n
, a
);
return 0;
}
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