Since that's the damage formula, I got 7526925 as the maximum damage though I might be wrong
It's Lickilicky +6 Explosion, STAB (I think STAB Explosion from Lickilicky outweighs Explosion from Metagross, regardless of it's higher attack stat), flower gift x2, helping hand x2, skill swap with pure power, critical hit, hitting a level 1 happiny with minimum defense stat (-6)