1/21+202/2121+50505/212121+13131313/21212121
=1/21+(2*101)/(21*101)+(5*10101)/(21*10101)+13*1010101/(21*1010101)
=1/21+2/21+5/21+13/21
=1
1/21+202/2121+50505/212121+13131313/21212121
=1/21+(2*101)/(21*101)+(5*10101)/(21*10101)+13*1010101/(21*1010101)
=1/21+2/21+5/21+13/21
=1