garyng

头尾各一半 × 项数

@echo off
set start=1
set n=100
set different=1
echo 公差：%different%
echo 项数：%n%
echo 头：%start%
set /a last = %start%+%n%*%different%-1
echo 尾：%last%
set /a sum=(%start%+%last%)*%n%/2
echo 和：%sum%
pause
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