规律是:2+4+6+……+2*n=n*(n+1)
(2000+2)+(2000+4)+(2000+6)+(2000+8)+……+(2000+50)
=2000*25+ 2+4+6+8+……+50
=50000+(50/2)*(50/2+1)
=50650
规律是:2+4+6+……+2*n=n*(n+1)
(2000+2)+(2000+4)+(2000+6)+(2000+8)+……+(2000+50)
=2000*25+ 2+4+6+8+……+50
=50000+(50/2)*(50/2+1)
=50650