1×3×5+3×5×7+5×7×9+…+101×103×105
=1*3*5+(3*5*7*9-1*3*5*7)/8+(5*7*9*11-3*5*7*9)/8+...+(101*103*105*107-99*101*103*105)/8
=1*3*5+(101*103*105*107-1*3*5*7)/8
=15+(116877705-105)/8
=15+14609700
=14609715
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原理:
n*(n+2)*(n+4)=[n(n+2)(n+4)(n+6)-(n-2)n(n+2)(n+4)]/8