(1)1+3+5+7+9+.+(2n-1)+(2n+1)+(2n+3)=[(2n-3+1)/2]^2=(n-1)^2=n^2-2n+1
(2)103+105+107+109+.+2003+2005=[(2005+103)/2]^2=1110916
1+2+3+4+5+6+7+8+9+…+n=n(n+1)/2 1+3+5+7+9+11+13+15+…+(2n-1)=n
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