2/(1*7)=1/3*(1/1-1/7)
2/(7*13)=1/3*(1/7-1/13)
…………
2/(1*7)+2/(7*13)+2/(13*19)+...+2/(145*151)
=1/3*(1/1-1/7+1/7-1/13+1/13-1/19+……+1/145-1/151)
=1/3*(1-1/151)
=50/151