My math indicates 1944 + 405% AP based on the Wiki's numbers. Unless I'm understanding something wrong, each wave of missiles can hit a champion for "Initial Magic Damage" once, plus "additional non-minion damage" 4 times, with "additional non-minion damage" being equal to 20% of "Initial Magic Damage". In other words, the base damage is Initial damage of the normal W (180) plus 4 times the initial damage of the RW (4x225 = 900), add them together (900 + 180 = 1080) and add 80% (1080x1.8) to get 1944. Then the same with the AP ratios (45% on both W and RW; 5x.45 = 2.25; 2.25x1.8) to get 405% AP.