2x1=2
2x2=4
2x3=6
2x4=8
2x5=10
2x6=12
2x7=14
2x8=16
2x9=18
2x10=20
2x11=22
2x12=24
2x13=26
2x14=28
2x15=30
2x16=32
2x17=34
2x18=36
2x19=38
2x20=40