A106003 Keep only the middle digit of each integer and concatenate them. The result is the concatenation of all integers of the sequence.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 110, 111, 200, 210, 211, 212, 220, 300, 400, 420, 510, 600, 620, 710, 711, 720, 810, 820, 822, 823, 900, 930, 10000, 10001, 10400, 11000, 11001, 11400, 12200, 13000, 13500, 14100, 15000, 15600, 16000, 16001, 16600, 17200