Tính

S3 = 21 + 23 + 25 +....+ 1001

S4 = 24 + 25 + 26 +....+ 125 + 126

S5 = 1 + 4 + 7 +.......+ 79

S6 = 15 + 17 + 19 + 21 +....+ 151 + 153 + 155

S7 = 15 + 25 + 35 +....+ 115