题解 | #等差数列#
等差数列
http://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
import sys
for line in sys.stdin:
a = line.strip()
n = 0
sum = 0
for i in range(1, int(a) + 1):
n = 3*i - 1
sum = sum + n
print(sum)
# print(int(a[0]) + int(a[1])) 
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