题解 | #等差数列#
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
#num=n*(a1+an)/2 = n(2+n*3-1)/2 = (3*n*n-n)/2 n=int(input()) print(int((3*n*n+n)/2))
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
#num=n*(a1+an)/2 = n(2+n*3-1)/2 = (3*n*n-n)/2 n=int(input()) print(int((3*n*n+n)/2))
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