题解 | #等差数列#
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
#include <stdio.h>
int main() {
int a,b,n,all;
scanf("%d",&n);
all=0;
for(a=1;a<=n;a++)
{
all=all+3*a-1;
}
printf("%d",all);
return 0;
}
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