题解 | #等差数列#
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
#include <stdio.h>
#include <math.h>
int main(){
int n;
const int A1 = 2;
const int D = 3;
scanf("%d", &n);
int sn;
sn = ((float)n / 2) * (2 * A1 + (n - 1) * D);
printf("%d", sn);
return 0;
}
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