The activity number is determined in this way: time = number of two-week periods in which you've posted since your registration activity = min(time * 14, posts)
1 X 14 = 14 2 X 14 = 28 3 X 14 = 42 ( jr member) 30days-42days 4 X 14 = 56 5 X 14 = 70 (member) 60days -70days 6 X 14 = 84 7 X 14 = 98 8 X 14 = 112 9 X 14 = 126 (full member) 120days-126days 10 X 14 = 140 11 X 14 = 154 12 X 14 = 168 13 X 14 = 182 14 X 14 = 196 15 X 14 = 210 16 X 14 = 224 17 X 14 = 238 18 X 14 = 252 (Senior Member) 252days