题解 | #等差数列#
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
a =int(input()) sn = a*2+(a*(a-1)*3)/2 print(int(sn))
等差数列求和公式
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
a =int(input()) sn = a*2+(a*(a-1)*3)/2 print(int(sn))
等差数列求和公式
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