[seqfan] Just for fun, more tennis balls

[David Scambler]

On turn n ball 2n-1 is introduced to the room, ball 2n is introduced to the garden, then one of the balls in the room is swapped with one of the balls in the garden.

After turn n

Combinations = 1,4,18,68,250,922,3430,... ( equals A115112 except 1st term )
Total on lawn = 1,20,190,1226,6878,35962,180080,...
Total in room = 2,20,188,1222,6872,35954,180070,...