1|4+1|28+1|70+1|130+1|208+1|304

问题描述:

1|4+1|28+1|70+1|130+1|208+1|304

1/1*4+1/4*7+1/7*10+1/10*13+.
1/3(1-1/4+1/4-1/7+.+1/16-1/19)
=1/3*18/19
=6/19