Răspuns:
aa = 10a + a = 11a
abab = 1000a + 100b + 10a +b = 1010a + 101b
x0yx = 1000x + 100 · 0 + 10y + x = 1001x + 10y
xyyx = 1000x + 100y + 10y + x = 1001x + 110y
2a3a1 = 2 · 10000 + 1000a + 3 · 100 + 10a + 1 = 20000 + 1000a + 300 + 10a + 1 = 20301 + 1010a
1bb20 = 1 · 10000 + 1000b + 100b + 20 + 0 = 10020 + 1100b
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