What number comes next.. {18151511}, {111409070820}, {020919081516}, {11091407}, {?}

[spoiler intro="Solution"] The alphabets are assigned numbers from 01 to 26
a=01, b=02, c=03.. z=26. Then the chess pieces are coded and placed on the order in which they are placed at the start of each game.

ie- rook = 18151511
knight = 111409070820
bishop = 020919081516
king = 11091407

Logically, the next would be queen which is = {1721050514}

[/spoiler]