2594 - C二级辅导-等差数列

2

7

Solution C

#include <stdio.h>

int sum(int n) {
    int s = 0;
    do {
        s += n;
    } while (n --);
    return s;
}

int main() {
    int n;
    scanf("%d", &n);
    printf("%d\n", 2 * n + sum(n - 1) * 3);
    return 0;
}

Solution C++

#include <stdio.h>
int a[100000];
int main()
{
	int n;
	while(scanf("%d",&n)!=EOF)
	{
		long long sum=2;
		for(int i=1;i<n;i++)
		sum+=i*3+2;
		printf("%lld\n",sum);
	}
	return 0;
}