1.(2+5+8+...+2000)-1+4+7+...1999 (2000-2)/3+1-1=666解法一;(2+1999)+(5+1996)+.+(1997+4)+(2000-1)=2001+2001+.+2001+1999=2001*666+1999=1332666+1999=1334665解法二;(2-1)+(5+4)+(8+7)+.(2000+1999) (3999-9)/3+1=666=1+(9+15+21+.+3999)=1+(3999+9)*666/2

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